



LIBRARY OF CONGRESS. 

% . 

Shelfi$j£L 

UNITED STATES OF AMERICA. 


















SOME ESSENTIALS OF 
PHYSICS 



M. L. SEYMOUR and WASHINGTON WILSON 
•t « 

OF THE STATE NORMAL SCHOOL, CHICO, 
CALIFORNIA 




( Ah- 10 IBS' 5 

- &7y (jr , ' 

CHICAGO 


A. FLANAGAN, PUBLISHER 


X 








COPYRIGHT, 1893, 

By M. L. SEYMOUR AND WASHINGTON WILSON 


Etye ILakcsttie 

R. R. DONNELLEY & SONS CO., CHICAGO 




PEEFACE. 


The purpose of this book is to guide the pupil in his 
efforts to know more of nature and her phenomena. 

No experiment or suggestion is offered that has not been 
repeatedly tested in class work. 

The time has passed for the Experimental Lecture Course 
before young people anxious to do just such things themselves. 

Only one way seems open to the Science Student, i. e ., 
Nature's Way — by experience, 

The one thing to do more than all others in all our schools, 
is to beget in our pupils the power to think accurately— 
persistently. 

The next most important thing to acquire is clear, truthful 
expression. 

All true work in science is especially helpful on these 
points. 

The description of the experiment, its phenomena and 
proof, are carefully omitted. 

It is hoped the cuts and statements concerning them will 
prove plain enough to show the pupil what to do, and give 
some hint as to how to do it. 

The object has been to state and show the essentials of 
the topic. Hence it is presumed the library or teacher's desk 
is supplied with fuller texts on the subject. 

The teacher must precede his pupils in all experimental 
work. He must be sure that he has worked the ground all 
over before directing others. 


3 



4 


PREFACE. 


Success will be assured if the teacher can create in the 
minds of his pupils a spirit of investigation, if he can chal¬ 
lenge them by questions, by drawings, to sharpest thinking— 
and by skillful handling of the class use the friction of one 
mind upon another as a stimulus to quick insight. 

A student who successfully performs one experiment, 
clearly describing it and logically stating its phenomena and 
what it proves, has gained more power than he could ever 
acquire by seeing others do it. 

Certain topics are outlined by carefully prepared defini¬ 
tions, drawings and statements—others are given in outline 
without comment. 

It is hoped the simple character of the drawings will lead 
to their reproduction. 

Some of them are from the valuable works of Atkinson, 
Lodge, Shaw, Poyser, Avery, Hopkins, Deschanel, Silliman, 
Mendenhall, and Gage. 

These drawings, with many original ones, are from the pen 
of the artist, Miss Marie Pioda, Santa Cruz, Cal. 

Minor L. Seymour. 

Chico, California, Washington Wilson, 

Jan. 1, 1893 . 


INDEX 


Adhesion, 

Alcohol, 

Aluminium, 

Ampere, 

Apple corer, 

Arc light, 

Artificial magnet, - 
Aspirator, 

Atom, ... 
Baking powder, - 
Balls, 

Barometer, - 
Battery, 

care of, - 
construction, 
cutting of plates, 
current in, 
kinds of, 
liquid for, - 
principles of, - 
setting up, 
Berrenberg pump, 
Call bells, 

Candle, 

Capstan, 

Chemical affinity, 
Cohesion, 

Compass, 
Conductivity, 
Conductor, - 
Cords, 


PAGE 


Cork, .... 39 

Current, 12 

Cutting of bottle, - 40 

Dip of needle, - - 84 

Diplex, - - - 132 

Duplex, - - - 132 

Dynamic electricity, - 110 

Dynamo, - - - 148 

alternating current in, 150 
brush, - • - 153 

field magnets, - - 152 

commutator, - - 153 

direct current, - - 151 

principles of, - - 148 

rheostat, - - - 161 

shunt, - - - 154 

Electroscope, - - 90 

Electrotyping, - - 144 

Element, - - - 113 

Energy, ... 49 

Envelope, - - 42 

Eraser, ... 42 

Eudiometer, - - - 105 

Excitant, ... 87 

Exploder, - - - 137 

Egg, .... 57 

Electricity, 86 

Electric discharge, - 106 

machine, 98 

measurements, - 119 


potential, 89 


PAGE 

41 

37 

146 

120 

58 

134 

67 

53 

42 

44 

36 

50 

111 

118 

114 

115 

113 

113 

116 

113 

116 

136 

126 

37 

28 

47 

41 

82 

94 

94 

17 





6 


INDEX. 


Electric street car, 
welding, 
spark, 
brush, 

Electro magnet, - 
magnetic, 
thermal effects, 
Electrophorus, 
making, 

explanation of, - 
Electrolysis, 
cup, 

Electromotive force, 
Electroplating, 

Falling bodies, 

Fire alarm, 
self-acting, 

Force, 

Frictional electricity, 
Fulcrum, 

Funnel, 

Goblet, 

Gravity, - 
Heat, - 
Horseshoes, 
Hydrostatics, 
Hydraulics, 
Incandescent lamp, 
Inclined plane, 
uses of, - 
Induction, 

Induction coil, 
Insulators, 
influence of, 

Ivory balls, 

Lath,. 

Lenz’s Law, 

Lever, 

compound, - 


PAGE 

Lever material, - - 9 

mathematical, - - 9 

orders of, - - 11 

Leyden jar, 99 

explanation of, - 101 

Light, 64 

Lines of force. - - 73, 93 

Lime water, 43 

Machine, ... 58 

Magnet, 67 

making, - - - 70 

cautions, 77 

keeping, ... 71 

theory of, - - - 77 

Magnetic field, - - 73 

meridian, 82 

Magnetism, - - 66 

Madgeburg hemispheres, 57 

Marble, - - - 39 

Matter, ... 35 

Mercury, - - - 52 

Microphone, - - 129 

Molecules, 42 

Mortar, ... 35 

Motor, .... 158 

Motion, ... 45 

Motorman, - - - 160 

Morse alphabet, - 131 

Moments of force, - - 12 

Molecular attraction, - 47 

Nails, .... 37 

Natural magnet, - - 67 

Needle, 69 

Newton, ... 72 

Non-conductor, - - 94 

Ohm, - 120 

Plaster of Paris, - - 44 

Pneumatics, - - 50 

Portative magnetism, - 81 


PAGE 

159 

138 

106 

106 

122 

122 

133 

96 

97 

98 

140 

140 

120 

145 

48 

127 

127 

46 

86 

1 

38 

44 

47 

61 

79 

58 

60 

135 

26 

26 

108 

132 

59 

109 

39 

89 

150 

10 

14 



INDEX. 


7 


Potential, 

PAGE 

- 49 

Potential difference, 

121 

Power, 

- 46 

Power distance, - 

10 

Prime conductor, 

103 

Pulley, 

- 15 

Pulley, fixed, 

16 

law, 

17,19 

movable, 

16 

system, 

- 17 

Yale, 

20 

Proof plane, ~ - 

- 98 

Razor, - 

125 

Reduction, 

- 145 

Repulsion, - 

89 

Residual magnetism, 

- 157 

Resistance, - 

120 

Rheostat, 

- 161 

Saturation, - 

71 

Screw, 

- 31 

law, 

32 

application, 

- 33 

Selective power, - 

75 

Silent discharge, 

- 

Shunt, - 

154 

Sound, 

- 62 

Specific gravity, - 

59 

Spoon, 

- 43 


Suggestions, 

PAGE 

34, 35 

Sucker, 

- 54 

Superstition, 

78 

Standard, 

- 89 

Static electricity, 

102 

Stereotype plates, - 

- 144 

Storage batteries, 

146 

Strength of magnet, 

- 75 

Straw, ... - 

55 

Synthesis, 

- 143 

Telegraph, - 

130 

Telephone, 

- 129 

Tension, 

17 

Thermostat, 

- 128 

Terrestrial magnetism, 

81 

Transformer, - 

- 151 

Trolley, 

159 

Variation, 

- 82 

Volt, - 

120 

Vortex rings, 

- 40 

Vulcanite, 

92 

Watt, 

- 120 

Wedge, 

30 

uses, 

- 31 

Weight distance, - 

10 

Wheel and axle, 

22 

law of, 

22 





MECHANICS. 


CHAPTER I. 

THE LEVER. 


F 



Fig. 1. 


With suitable stick, weight, and rest, illustrate the 
above drawing. 

Explain the terms used and point them out in the 
illustration. 

By measurement, and from the text-book, determine 
the unknown weight. 

Disturb the equilibrium of the lever and note the rel¬ 
ative distances through which the power and weight move. 
Note also the relative velocities of each. 

From the above experiments complete the following 
proportions: 1) P : W 2) Dist. W moves : Dist. 

P moves 3) V. of P : V. of W :: ? : ?. 

Change the completed proportions to equations. 

Notice that the ratio between the distances or velocities 
of power and weight is the ratio between them, also. 

In the affairs of life the lever is a material one. 

The material lever is a rigid bar moving about a support 
called the fulcrum. 

In all problem work, the lever is mathematical. 

A mathematical lever is a line free to move about a point. 





10 


THE LEVER. 


FORMULA FOR TERMS. P = Power. F = Fulcrum. 

PD = Power-distance. W = Weight. L= Lever. WD 
= Weight-distance. 

The power-distance is the perpendicular distance from 
the fulcrum to the line along which the power acts. 

The weight-distance is the perpendicular distance from 
the fulcrum to the line along which the weight acts. 

In applying the mathematical lever to the material one, 
an error arises, viz: the difference in the weight of the 
arms, whatever their position. Thus,— 



From the above drawing it appears that the power and 
weight distances change with the position of the lever. 

All measurements are from the fulcrum. 










THE LEVER. 


11 


The fulcrum is a point or line about which a lever 
turns. 

There are three orders of the lever: 

First order. The F is between the P and the W. 


r 

p 

Second order. 

V 

t 

* <S 

w 

Fig. 2. 

The W is between the F and the P. 

F 

Third order. 

& A 

W 

Fig. 3. 

The P is between the F and the W. 

s 

t 

F 



w 

Fig. 4. 


The first and second orders of levers effect an exchange of 
velocity for intensity. These orders of levers appear in many 
simple inventions in which it is desired to gain power at a 
loss of time or velocity. Levers of the third order effect an 
exchange of intensity for velocity, always at a loss of power. 
This is strikingly illustrated in the locomotion and flight of 
animals. 

Classify: Crowbar, steelyard, wheelbarrow, sugar 





12 


THE LEVEE. 


tongs, nutcracker, scissors, sheep shears, transom lift, 
lemon squeezer, desk seat, pump handle, pincers, claw 
hammer, store truck, and door. Show how the last may 
illustrate each of the orders of levers. 

A general formula for the solution of all problems on 
the lever is: 

P x PD = W X WD. 

This, however, considers the lever as statical, and as 
such it may be better understood as illustrating the law 
of the 

MOMENTS OF FORCE. A moment of force is the product 
of the numbers representing the power or weight and the per¬ 
pendicular distance of the same from the fulcrum. Hence the 
solution of all problems on the lever calls for an equality of 
the moments of force. Further, any three of the elements of 
the lever being given, the fourth can be found. Before any 
motion can result, the equilibrium of the lever must be dis¬ 
turbed. 

ILLUSTRATIVE PROBLEMS. 

1 . In a lever 8 ft. long, a power of 6 lb. will balance 
what weight 6 in. from the fulcrum? 

2 . How much power will balance one ton on a 12-ft. 
lever with the fulcrum 3 in. from the weight? 

3. Where place the fulcrum so that a power of 2 lb. 
may balance 100 lb. on a lever 9 ft. long? 

4. A and B carry a 10-lb. salmon on an 8-ft. pole. 
The fish is 6 in. nearer A than B. What does each carry? 

A PRACTICAL PROBLEM. 

Three men wish to carry an equal weight of a stick of 
timber of uniform size and density. Where place a cross¬ 
lever for A and B, C being at the end of the stick? 

EXPERIMENT. Secure a steel rod of uniform size 
and of convenient length. On each of two scales that 



THE LEVER. 


13 


turn easily at the weight of a grain, balance a narrow- 
edged support. 

Load one of the scales with one-third and the other 
with two thirds of the weight of the rod. Place one end 
of the rod on the support of the scale bearing one-third its 
weight. Adjust the other scale and its support so that 
both scales will be in equipoise. 

Upon measurement it will be found that the support 
bearing the greater weight is at a point one-fourth the 
length of the rod from its end. 

SOLUTION. Consider the stick a mathematical lever 
with its weight massed over a fulcrum at its center. 

*_©_ c 

5 

B 

Fig 5. 

It is required to distribute this weight so that its one- 
third shall be at C and its two-thirds at some point be¬ 
tween A and B, the equilibrium remaining undisturbed. 



B 

Fig. 6. 


The lever is of the first order. 

Since the ratio between W and P is 2 , the power arm is 
twice the weight arm. 

The power arm is one-half the length of the stick. The 
weight arm is therefore one-fourth the length of the stick. 

The cross-bar must be placed one-fourth the length of 
the stick from its fulcrum. 




14 


THE LEVER. 


Where should the cross-lever be placed for A and B to 
carry three-fourths of the weight ? In a manner similar, 
the position will be found at one-sixth the fength of the 
stick from its fulcrum. Give the solution. 

THE COMPOUND LEVER. A compound lever is a 
combination of simple levers. 

The weight for one lever becomes the power for the 
next. Thus: 

4ff - 3,n i _ V Sft. 4 in. 

i r 

Fig. 7. 

What power is required to disturb the equilibrium ? 

MISCELLANEOUS PROBLEMS. 

1. L = 20 ft., P = 100 lb., W = 400 lb., F= ? 

2 . W = 2000 lb., L = 30 ft., F is 6 in. from end, 
P= ? 

3. L = 36 ft., W = 1000 lb., P = 25 lb., PD and 
WD = ? 

4. IIow long is the lever if 500 lb. balance 40 lb. 6 
in. from the fulcrum? 

5. What are the P and W distances if 16 lb. balance 
400 lb. on a 20-ft. lever ? 

6 . The oar of a boat is 8 ft. long. The hand is 2 ft. 
from the row-lock. Man and boat weigh 600 lb. Give P. 

7. Two weights, 5 lb. and 7 lb., balance each other 
on the extremities of a lever 10 ft. long. Where is the 
fulcrum? 

8 . Four weights, 2, 4, 8, and 6 lb., the first and last at 
the ends, are so placed as to be at equal distances apart on 
a 19-ft. lever. Where place the fulcrum for equilibrium? 





THE PULLEY. 


15 


9. Four hundred lb. are carried on a pole 16 feet 
long, supported on the shoulders of A and B. The 
weight is 2 ft. nearer A than B. What does each carry? 

10 . A beam 27 ft. long is supported at each end. At 
8 ft. from one end is a weight of 800 lb. Four feet from 
the other end is a weight of 600 lb. What weight is 
carried by each support ? 

11. A lever of uniform size and density is 40 ft. long 
and weighs 400 lb. It is supported by two props, A and 
B; the former is 2 ft. from one end and the other is 6 ft. 
from the other end. What weight is carried by each ? 

12. In a lever of the third order 9 ft. long, with the 
dcrum at one end and 100 lb. weight at the other, where 
ace a power of 120 lb. for equilibrium ? 

13. What is gained by a lever of the third order? 
ustrate. 

14. V. of P is to V. of W as 7 is to 1. The lever is 

ft. What are its arms ? 

15. A roll of butter weighs 1^ lb. on one pan of a 
’ dse balance and 2 lb. on the other. What is the true 
1 eight ? 

CHAPTER II. 

THE PULLEY. 

Suspend a common pulley and over it pass a cord. To 
|pach end of the cord attach a brick. Observe that as 
pressure is applied to raise or lower either brick, equal 
lengths of the cord pass on and off the pulley. Hence, the 

LAW OF THE PULLEY. The weight is as many times 
the power as the distance through which the power moves is 
times the distance through which the weight moves. 

Flexibility of cord and friction are here disregarded. 


16 


THE PULLEY. 


A simple fixed pulley is a grooved wheel turning upon 
an axle. In its action it is a lever of the first order hav¬ 
ing equal arms. Hence no mechanical advantage can arise 
from its use. The fixed pulley changes the direction of 
the power. 

EXPERIMENTS. 1. Arrange a fixed pulley so that a 
downward pull of the rope may raise a bucket of water. 

2 . Arrange two fixed pulleys so that a horse may raise 
by a horizontal pull on a rope a hod of mortar to the top 
of a building. 

Show the above by actual arrangement and by drawing. 

THE MOVABLE PULLEY. Pass a cord from a movable 
pulley bearing a weight to and over a fixed pulley as 
shown below: 



Fig. 8. 


Determine the ratio between the distances through 
which the P and W move; also between the P and W. 

From the work already done on the lever it will be 
seen that the movable pulley is a lever of the second 
order, the diameter of the pulley being the power- 
distance and its radius the weight-distance. Locate the 
fulcrum. 









THE PULLEY. 


17 


The size of all pulleys has direct reference to the flex¬ 
ibility of the cord. 

It should be remembered that the efficient agent is the 
cord, and not the pulley, for excepting wear and friction a ring 
would do as well. 

From the above it will be seen that a cord is a machine 
for transmitting force in any direction, while a lever can 
move a weight to or from the power only. 



Fig. 9. 


In the above diagram the movable pulley is supported 
by three parts of the cord, and, as the tension on each 
equals the power, the weight is three times the power. 

In the former system the weight is supported by two 
parts of the cord; hence it is twice the power. In this 
system the weight is supported by three parts of the cord; 
hence it is treble the power. 

In any system of pulleys having a continuous cord, the 
weight equals the sum of the tensions upon the parts of the 













18 


THE PULLEY. 


cord, and the number representing the parts of the cord is the 
ratio between the power and weight. 

This ratio may be used in the solution of problems. 

PROBLEM. 

Thirteen lb. may be supported by what power with a 
continuous cord, one movable and two fixed pulleys. 

There are three parts of the cord. 

Weight is three times the power. 

Power is 414 lb. 

The power is 4 lb. with one movable and one fixed 
pulley. What is the weight ? 

The efficiency of any system having a continuous cord 
is increased by attaching the fixed end of the cord to the 
movable block. Why ? Try it 



Fig. 10. 










THE PULLEY. 


19 


The system shown has four movable pulleys, each 
with a separate cord. The pulley A serves to change 
the direction of the power. ... 

The tension on the hook at B is the sum of the ten¬ 
sions at A and C ; hence twice the power. This system 
gives a great gain of power at the expense of range. 

The value of such a system is in the doubling of the 
effect of the power at each successive movable pulley. 

Raise 2 to the power indicated by the number of movable 
pulleys. This number is the ratio between power and weight 
and may be used to find either when the other is given. 

Show by diagram a system of one fixed and three 
movable pulleys with separate cords. 

PROBLEM. 

In the above system what power will sustain a weight 
of 144 lb.? 

Ratio between power and weight is 8. 

Weight is 8 times the power. 

Power is 18 lb. 

Pulleys, however arranged, can give mechanical ad¬ 
vantage by exchange only. These exchanges are limited 
to direction, velocity, distance, time and tension. 

Show how a sewing machine exchanges intensity for 
velocity. Explain the exchange in the case of the wind¬ 
mill pump, the threshing machine, the coffee mill. 

What pulley would you use for raising a bucket of 
water from a well ? What system for raising a load to 
the top of a building with a horse ? What system for 
pulling a safe up a stairway ? 

THE YALE PULLEY. This is a pulley manufactured 
by the Yale Lock Conipany. Its two points of excellence 
are: 


20 


THE PULLEY. 


1. The weight remains suspended at any point to 
which it has been hoisted. 

2. A great ratio is obtained between the power and 
the weight. 

This machine consists of a fixed pulley, having two 
grooves of unequal circumferences and a movable pulley, 
over both of which is passed an endless chain. 



Fig. 11. 


A is the single wheel with two grooves upon it. 

The grooves are notched to receive the links of the 
chain, 










THE PULLEY. 


21 


Groove b is the circumference of a circle whose diam¬ 
eter is a little less than at c. 

Suppose groove b to be 10 in., and groove c to be 12 
in., from b to e. 

Let the power at 1 be lowered 12 in. Chain 2 moves 
up 12 in., while chain 3 moves down 10 in., lifting the 
weight 1 in. 

The ratio between the power and the weight is 12. 

It is evident that this ratio may be increased by mak¬ 
ing less the difference between the length of the grooves 
upon the wheel A. 

In most other pulleys the weight runs back when the 
power is removed. 

Through the action of gravity, it is evident that the 
line of direction does not pass through the center of wheel 
A, but does pass midway between chains 2 and 3. 

Since the chain cannot slip, the weight therefore re¬ 
mains suspended. 


CHAPTER III. 

THE WHEEL AND AXLE. 


Attach one end of a cord to the axle of a grindstone 
and the other end to a weight. On turning the crank a 
large load may be easily lifted. The presence of the 
stone need not mislead the pupils. 

The wheel and axle is a modified form of both lever 
and pulley. The lever appears in the unequal arms of the 
wheel and axle, and the pulley in its most efficient agent, 
the cord. 



If the application of the power is at the circumference of 
the wheel or axle, there is a lever of the first order, the ful¬ 
crum being the common axis, and the arms being the radii of 
the wheel and axle respectively. 

The wheel and axle is a machine of varying efficiency, 
due to the fact that whether the power is applied at the 
circumference of the wheel or axle, at two opposite points 

22 































THE WHEEL AND AXLE. 


23 


in each revolution the order of lever changes. With the 
power applied at the circumference of the wheel, the levers 
are of the first and second orders; with the power applied 
at the circumference of the axle, the levers are of the first 
aud third orders, as appears from the following diagrams: 



Diagram A. 




THE WHEEL AND AXLE. 










THE WHEEL AND AXLE. 


25 



Inability to give uniform motion to a grindstone or wind¬ 
lass in use is seen from the above diagrams to be due to the 
change of levers at each revolution. 

The law of the lever will apply to the wheel and axle 
when modified as follows: 

In any two circles the ratio between their radii, diam¬ 
eters and circumferences is the same; therefore, 

r : R 

P : W :: d : D 
c : C 

If the application of the power is at the circumference 
of the axle the proportions are, 






26 


THE INCLINED PLANE. 


R : r 
P : W :: D : d 
C : c 

The capstan is a wheel and axle in a vertical position 
and is used for moving heavy weights horizontally. 

It is evident that the above laws apply equally as well 
to the capstan. 

PROBLEM. 

The diameters of a wheel and axle are respectively 36 
and 4 inches. What power is required to support one ton? 

The ratio between power and weight is 9 . ' 

Weight is 9 times the power. 

Power is 222 f lb. 

The wheel and axle is a contrivance in which the lever 
and pulley appear in their greatest efficiency. 

Describe and exjdain the uses of the following: Wind¬ 
lass, capstan, car-brake, pilot-wheel, derrick, wheel-tape. 


CHAPTER IV. 


THE INCLINED PLANE. 



Observe that the top of the desk represents an inclined 
plane. 





THE INCLINED PLANE. 


27 


B 



AB represents the length of the plane, BC the height, 
and AC the base. 

The inclined plane is a smooth, unyielding, inclined 
surface. 

Like the lever it is used in raising heavy weights. 

The power may be applied in a direction parallel to 
the length of the plane, or parallel to its base. 











28 


THE INCLINED PLANE. 


In either case the height of the plane is the weight- 
distance. 

The power-distance is either the length of the plane or 
the length of its base. 

When the power acts in a direction parallel to the 
length of the plane, the ratio between its length and 
height is the ratio between the power and the weight. 

PROBLEM. 

What power is required to raise a barrel of flour into 
a wagon 4 ft. high on a ladder 12 ft. long? 

Let the power be applied in a direction parallel to the 
length of the plane. 

The ratio between the power and the weight is 3 . 

The weight is 3 times the power. 

The power is 65 lb. 

When the power acts in a direction parallel to the base 
of the plane, the ratio between its base and height is the 
ratio between the power and weight. 

PROBLEM. 

The base and height of an inclined plane are 20 ft. and 
2 ft. respectively. What power acting in a direction par¬ 
allel to its base will be required to support a ton? 

The ratio between the power and weight is 10 . 

The weight is 10 times the power. 

The power is 200 lb. 

The demonstration of these statements may be found 
in special text-books. 

The inclined plane has its greatest practical value in 
the skid, bridge, and viaduct. 

The chute is employed in moving logs down mountain 


TIIE INCLINED PLANE. 


20 


sides to the mill below, and again for raising them from 
the water to the saws. 

The greater the difference between the length and 
height of the plane, the less the power, the weight being 
the same. 

The highest utility of the inclined plane appears in 
flumes, water courses, pitch of roofs and gradients. The 
school boy knows the value of the incline from the use of 
roller skates and the express wagon. 

A street grade of 1 in 20 means that for every 20 ft. 
of advance there is a rise of 1 ft. 

A carriage on a smooth road will yield to gravity and 
descend when the grade is more than 1 in 20, but a rail¬ 
way car will do the same when the grade is 1 in 150. 
Why? 



Fig. 16. 

Let MLRS represent a street grade of 1 in 5. A horse 
with an inexperienced driver will be urged up the incline 
in the direction of the line AB. If left to himself he will 
take the zigzag course shown by the line CDE. Why? 

Engineers may have seen this act, for it is by length- 



30 


THE WEDGE. 


ening the plane by winding that railroads cross mountains. 
Nature thus indicates the direction of commercial routes 
by her water courses. 

Whenever the incline is so great that the force of 
gravity exceeds traction the grade is impracticable. 


CHAPTER V. 

THE WEDGE. 

Instead of moving a load on an inclined plane we may 
thrust an inclined plane under the load. From this it 
appears that the wedge is a movable inclined plane. Its 
use is to separate two surfaces that are pressed or drawn 
together. For such purpose the wedge is usually double. 

Examine the blade of a pocket knife. What kind of 
a wedge is it? 

With it make three wedges and illustrate the following: 



The simplicity and effectiveness of the wedge, whether 
single or double, makes it of great value. It appears in 
the edged tools of the mechanic and artisan. It is seen in 
the keystone of the arch of the mason, as well as in the 
plow and ax of the farmer. 

Name a dozen tools illustrating the wedge. 

The wedge works on the principle stated in the second 










TIIE SCREW. 


31 


case of the inclined plane. The length of the wedge rep¬ 
resents the base of the plane and its thickness, if single, 
the height of the plane. 

The wedge is moved by percussion. It is made to 
overcome the resistance by the friction of its surfaces. If 
it is too smooth or is oiled it is valueless. 

Since the ratio of a blow to a resistance cannot be 
easily estimated, the theory of the wedge has no practical 
value. Hence no problems on the wedge are given. 

As a machine the wedge is especially useful when it is 
required to exert a great force through a small space. 
Ships are raised in docks by wedges driven under their 
keels, and are launched by their removal. 

Wedges are used to straighten chimneys, to cleave 
timber, and press the oil from seeds. 

In the application of the principle of the wedge to 
tools, the strength of the tool is diminished as the angle 
is lessened. Approximately, the angle is 30° for cutting 
wood, 60° for iron, and 90° for brass. 


CHAPTER VI. 

THE SCREW. 

Examine a common screw and name its parts. How 
many times must the screw in hand be turned around to 
advance its length? The head of the screw has a crease 
by which it is turned. The threads upon it are inclined 
planes by which it is forced in or out. 

Cut from paper a right-angled triangle whose hypote¬ 
nuse is but little more than its base, and wind this triangle 
upon a pencil with its base at right angles to it, thus: 


32 


THE SCREW. 



Fig. 18. 


Notice that the exposed edges of the paper represent 
the threads of the screw, and the distance between them 
its pitch. 

The screw is a spiral inclined plane. It exchanges 
velocity for intensity and at a great rate. It is, therefore, 
among the most powerful of mechanical appliances. 

The nut is a short hollow cylinder whose inside thread 
fits into the spaces between the threads of the screw. 

Either the nut or the screw may be stationary. 

In problems upon the screw, beside power and weight, 
regard is had for two things only,—the distance through 
which the weight moves and the distance through which 
the power moves. 

While the weight moves through a distance equal to 







THE SCREW. 


33 


the pitch of the screw, the power moves through a dis¬ 
tance equal to the circumference of the circle which it 
describes. 

The ratio between the circumference of the circle 
which the power describes and the pitch of the screw is 
the ratio between the power and the weight. 

PROBLEM. 

What weight may be raised by a screw whose pitch is 
i in., and the lever in the head of the screw 5 ft. long, 
the power of 20 lb. being applied at the end of the lever? 

The ratio between the power and the weight is 2X5X 
3.1416X12X8, which is 3015.936. 

The power is 20 lb. 

The weight is 3015.936X20 lb., which is 60318.72 lb., or 
30.1036 tons. 

The common illustrations of the screw are: Carriage 
bolts, carriage screws, lag screws, interior of rifled guns, 
gimlets, bits, augurs, screw propellers, copy and cider 
presses, and jack screws of all forms. 

In concluding these simple and brief statements upon 
the mechanical powers, the suggestion is offered that the 
careful teacher will lead his pupils to the fullest illustra¬ 
tion and explanation of as many of the common appliances 
of life as possible. 

Some one or more of the mechanical powers will be 
found to appear in the simplest of tools, and it should be 
the aim of the teacher to see that observation is followed 
by interpretation and careful application. 

It is not too much to say that man has copied all the 
mechanical powers from nature. The lever appears in all 
animal movements. Infusoria, the rotifer and paramoe- 
cium illustrate the wheel. The principle of the cord and 



34 


THE SCREW. 

pulley is seen in the use of tendons, especially in the eye. 
Teeth, tusks, horns, hoofs, beaks, and claws show the 
origin of the inclined plane and wedge. 

Nature presents two kinds of screws, the right and 
left, as seen in the bean and the hop. 

Convenience dictates the right handed screw, owing to 
the custom of men. From the structure of the plant to 
the huge weapon of the narwhal, the screw appears not so 
much as a mechanical power as a form of tissue combining 
strength and beauty. Whirlwinds and water spouts, 
which work on the principle of the screw, are nature’s 
greatest illustrations of her efforts in producing an equili¬ 
brium of forces. 

MISCELLANEOUS PROBLEMS. 

1. A horse attached to the end of a 12 ft. lever of a 
capstan pulls 300 lb. The axle of the capstan has a radius 
of 6 in. What weight can be moved? 

2 . With 5 movable pulleys and separate cords, what 
power will be required to support 160 lb.? 

3. With a continuous cord, one fixed and two mov¬ 
able pulleys, what will a pull of 6 lb. support? 

4. The base of an inclined plane is 14 ft. Its height 
is 2 ft. What power acting parallel to the base will sup¬ 
port 90 lb. ? 

5. What weight can be held on an inclined plane 10 
ft. long and 2 ft. high with 80 lb. of power? (Two cases.) 

6 . A screw has 4 threads to the inch. A weight of 
6,000 lb. is to be raised. How long a lever is necessary 
with a power of 100 lb. ? 

7. From the palm of the hand to the elbow is 12 in.; 
from the elbow to the point of attachment of the muscle 
is 2 in. What muscular strain is necessary to raise a 10-lb. 
ball in the hand? 


MATTER AND ITS PROPERTIES 


35 


8 . An inspector finds a parcel on a grocer’s balance 
weighing 5 lb, on one pan and 4 oz. less on the other. 
What is the true weight? 

9. The scale beam of a certain steelyard is 30 in. from 
the bearing nearest its center. The distance between the 
bearings is f in. What weight at the end of the beam 
will balance a load of 50 lb. ? 

10. One arm of a teeter-board is twice as long as the 
other, the board being 12 ft. long. A boy weighing 45 
lb. sits at the end of the longer arm. Where must a boy 
weighing 120 lb. sit so that the two will be in equipoise? 

As in the preceding pages, treat the following topics, 
of which limited space forbids more than a mere outline. 

The following syllabi are intended as aids in the 
assignment of lessons by topics, to be studied from any 
text-book. 

In assigning lessons, the following points may be 
found helpful*. 

1 . The topic. 

2. The topic chosen should be a unit in itself. 

3. Cautions as to use of text-book, regarding what to 
study and what to omit. 

4 . An opportune time for the assignment of the lesson 
is at the beginning of the recitation. 

5. See that the topics are related. 


CHAPTER VII. 

MATTER AND ITS PROPERTIES. 


The following figures indicate Laboratory work. Each 
cut is intended to show how one or more of the properties 


36 MATTER AND ITS PROPERTIES. 

of matter may be clearly comprehended, leaving the pupil 
to decide what that property is and how he found it out. 
Pupils are expected to reproduce the drawings. 

Snap a card from under a marble over a bottle. 



Swinging balls. 



Fig. 20. 





















MATTER AND ITS PROPERTIES, 


37 


Shoot a candle through a board. 



Fig. 21. 

Put nails into a glass full of water. 



Fig. 22. 

Into a wine glass of alcohol put a like quantity of 
cotton. 



Fig. 23 . 


































38 




MATTER ANI) ITS PROPERTIES. 


Invert a goblet in water. 



Fig. 24. 


Pour water into a funnel inserted air tight into a bottle. 



Fig. 25. 


























MATTER AND ITS PROPERTIES. 


39 


Push a cork into a bottle and remove it. 



Fig. 26 . 



Drop an inked ivory ball on marble. 




Fig. 27 . 












































40 


MATTER AND ITS PROPERTIES. 


Vortex rings. (Put hydrochloric acid and ammonia 
in separate dishes in the box.) 


o 



Draw a wire back and forth around a cylindrical stick 
and then measure. 


Cut a bottle. 



Pig. 29. 



Fig. 30. 

DIRECTIONS. Confine the air in the bottle to be cut. 
Wrap yarn soaked in kerosene around the bottle near the 
































MATTER AND ITS PROPERTIES. 


41 


desired cut. Secure the ends of the yarn without a knot. 
Light the soaked yarn and hold the bottle horizontally 
and rotate. If there is yarn enough the bottle w r ill break 
without using water. 

If the bottle is thick a light scratch is favorable to the 
experiment. 

Show the mercury shower. 



Fig. 31. 

COHESION AND ADHESION. Cohesion is the force 
that aggregates molecules and resists their separation. 
Adhesion and capillarity are forms of cohesion. 

To which do the following belong ? Give reasons. 
Write upon the blackboard with crayon. 

Open a sealed envelope without cutting or tearing it. 




42 


PHYSICAL AND CHEMICAL CHANGES. 



Cut a rubber eraser with a dry blade. Try a wet 
blade. 



CHAPTER VIII. 

PHYSICAL AND CHEMICAL CHANGES. 

A physical change is a change in which the molecule is 
not decomposed. 

A chemical change is a change in which the molecule is 
decomposed. 

THE MOLECULE AND THE ATOM. A molecule is the 
smallest particle of matter that can be produced by physical 
means and can exist alone. 

An atom is the smallest particle of matter that can be pro¬ 
duced by chemical means and cannot exist alone. 

Perform the following experiments. Classify the 
changes and fully explain them. 


















PHYSICAL AND CHEMICAL CHANGES. 


43 



Let a silver spoon stand in whipped egg. 



Fig. 35. 



















44 


PHYSICAL AND CHEMICAL CHANGES. 


Make a ball of Plaster of Paris. 



Pig, 36. 


Pour water on baking powder. 



Pig. 37 


























MOTION. 


45 


Pour into a test-tube half full of water, one-third as 
much alcohol. Test for temperature. 



State and classify the changes in baking potatoes, 
making vinegar, bread, biscuit, butter. 


CHAPTER IX. 

MOTION. 

Motion is the change of position in any atom, molecule, or 
mass of matter. 

The molecules of a pebble are, at no two successive 
instants of time, in the same position respecting each 
other. If the pebble be thrown into the air, it occupies 






46 


MOTION. 


different positions in space from point to point in time. 
The earth in its revolution around the sun and a moving 
train on a track have at no two successive points of time 
the same positions in space. 

Discuss: 

Motion. 

(a) Kinds. 

(b) Laws. 

(c) Momentum. 

(d) Give illustrations. 

POWER. 

Power is that which itself begins, increases, or retards 
motion in any atom, molecule, or mass of matter. 

A rifle ball is hurled through space; a glacier or an 
avalanche slides down a mountain side; a planet is held in 
its course about the sun. These are manifestations of 
power. 

Power is a generic term—the most comprehensive 
used in dynamics. It includes force and energy. (See 
“Force and Energy,” by Grant Allen.) 

FORCE. 

Force is a power which aggregates atoms, molecules, or 
masses of matter. 

Oxygen and hydrogen atoms unite to form molecules, 
and these to form masses of water; a boulder crashes 
down a mountain side; a river rolls onward to the ocean. 
These are manifestations of force. 

Discuss: 

Force. 

1. Kinds. 

(a) Chemical affinity. 


GRAVITY. 


47 


(b) Molecular attraction. 

(c) Gravity. 

(d) Electrical attraction. 

2. Units. 

3. Result or work. 

Chemical Affinity is the force that unites atoms into 
molecules. 

Molecular Attraction is the attraction between molecules 
—whether alike or unlike. 

Gravity is the attraction between masses of matter. 

Electrical Attraction. This manifestation of force has 
been given the above place because of its increasing ser¬ 
vice to man. 

It, like electricity, is difficult to define. It may not 
be amiss to say that Electrical Attraction is the force existing 
between unequally electrified bodies. 

CHAPTER X. 

GRAVITY. 

Under this term are considered Falling Bodies and the 
Pendulum. 

FALLING BODIES. From the accompanying diagram 
deduce the following formulae, if 

g = effect of gravity or 32^- ft., 
t = time, 
v = velocity, 

d = distance for any second, 
s = sum of distances. 

FORMULA. 1. v — gt 

2. d = £g(2t-l) 

3. t = ± (2d+g) 

4. S =: |gt 3 


48 


GRAVITY. 


The formula for d when representing a half second is 
derived from, 

s = igt 2 

Substituting, s = 16 T ^xi 

Hence, d = 


o 



PENDULUM. Topics: Kinds, Motions, Real Length, 
Oscillations, Center of Oscillation, Vibration, Time of 
Vibration, Amplitude of Vibration, Laws, Formulae. 
Give problems. 

MISCELLANEOUS PROBLEMS. 

1. 100 lb. at the surface of the earth will weigh how 
much 50 miles below the surface? 

2. How far will a body fall during the third Second? 

3. How long will it take a body to fall 100 ft.? 

4. Through what distance will a body fall in 7£ seconds? 

5. How long will it take a body to fall 579 ft.? 














ENERGY. 


49 


6. A body is thrown vertically upward 100 ft. How 
many seconds will elapse from its leaving the earth to its 
return? 

7. How long is a pendulum which beats once in two 
seconds? 

8. How often will a pendulum beat that is 4.35 in. long? 

9. What is the final velocity of a falling body at 
the end of the seventh second? 

10. A body falls 700 ft. in 6 seconds. What was its 
initial velocity? 


CHAPTER XI. 

ENERGY. 

Energy is a power which separates atoms, molecules, or 
masses of matter. 

The energy of heat separates particles of matter in 
explosions. Muscular energy may be stored up in a sus¬ 
pended ball, which expends it on being separated from 
the point of support. 

The heat energy of the sun stored up in coal may be 
transmitted to water, then to steam, and afterward appear 
in the working engine, the rotating spindle, and the mov¬ 
ing fabric. 

MODES OF ENERGY, (a) Potential. 

(b) Kinetic. 

Potential energy is the statical separation of portions of 
matter. 

A hanging lamp, confined steam, a stone on a mount¬ 
ain top are illustrations. 

Kinetic energy is the energy of motion, as the flying 
of a bird or the spinning of a top. 

These modes of energy are interchangeable. Show it. 


50 


PNEUMATICS. 


CHAPTER XII. 


PNEUMATICS 


This division of Physics affords ample scope for orig¬ 
inal experimentation. 

It has been found a profitable exercise for students to 
come before the class and perform and explain experiments 
as a teacher would do. The presence of the teacher, the 
questions of -the class, and the natural pride of the student 
are all powerful stimuli for developing the best efforts of 
the experimenter. 

It is presumed that, in such a course, the experiments 
have been previously assigned to individuals or to the 
class as a whole. 

The following figures illustrate easy experiments that 
may be profitable when performed, represented, and ex¬ 
plained. 

Perform the barometer experiment. 




Fig. 40. 







PNEUMATICS. 


51 


Same experiment after lifting the tube of mercury 
from the bowl. 



Fig. 41. 


Same experiment with the tube in an oblique position. 



Fig. 42. 









52 


PNEUMATICS. 


Perform the same experiment as shown in the cut 
below. 



Fig. 43. 





















PNEUMATICS. 


53 


THE CHAPMAN ASPIRATOR. This instrument may 
be understood from the drawing. 

Its chief use is in rapid filtering and in exhausting air 
by means of flowing water. A head of 30 ft. gives good 
results. 



















54 


PNEUMATICS. 


The sucker. 



Place a brick flatwise in a dish filled with water. 



Apply the palm of the hand to a piece of paper placed 
upon a goblet full of water. Invert the goblet and remove 
the hand. 





















PNEUMATICS. 


55 




Fig. 47. 


Drink through a straw from a glass of water. 



Burn a piece of paper in a goblet inverted over water. 




















56 


PNEUMATICS. 


Fill the larger jar with water. Cover with water the 
sliced potatoes in the smaller jar. Exhaust the tube. 

; 



8 


Fig. 50. 





















PNEUMATICS. 


57 


With an air pump perforin the following experiments: 
Drill a hole in the small end of a fresh egg and use as 
shown in Fig. 51. 



Magdeburg hemispheres. 


(Give history.) 



What is the air pressure on the hemispheres if their 
inside diameter is 4 in. and the vacuum is £ perfect? 













58 


M ACHINES. 


Place a perfect apple on the end of a tin apple corer 
and connect to the air pump, as shown below. 



TOPICS. Barometer, Manometer, Baroscope, Torri¬ 
celli’s Experiment, Mariotte’s Law, Sprengel’s Air Pump. 


CHAPTER XIII. 

MACHINES. 

1. Definition. 

2. Kinds, a) simple, b) compound. 

3. Uses. 

4. Friction, a) kinds, b) causes, c) facts. 

HYDROSTATICS. 

1. Definition. 

2. Incompressibility of liquids. 

3. Pressure, a) upward, b) downward, c) lateral, d) ma¬ 

chines, e) laws, f) problems. 

4. Liquids at rest, a) equilibrium—communicating vessels, 

b) water supply of your city, c) capillarity—capil¬ 
lary tubes—phenomena, d) buoyancy of liquids, 
e) Archimedes’ principle and experiments, f) float¬ 
ing bodies, g) laws, h) problems. 









SPECIFIC GRAVITY. 


59 


SPECIFIC GRAVITY. 

1. Definition. 

2. Standards, a) water, b) air, c) hydrogen. 

3. Problem, a) dividend, b) divisor, c) quotient. 

4. Hydrometers, a) constant weight, b) constant volume, 

c) for light and heavy liquids. 

PROBLEMS. 

1. A stone weighs 300 lb., its specific gravity is 2.5. 
What will it weigh in water? 

2. What will 12 oz. of gold weigh in alcohol whose 
specific gravity is .8? 

3. A piece of lead weighs 120 gr. in air and 109 gr. in 
water. What is its specific gravity? 

4. A fresh egg in. a pint of water sinks. How much 
salt must be added to the water to float the egg? What 
Jo salt is the water? (A saturated solution of salt is 100 ft 
salt.) 

5. A piece of cork displaces 2 lb. of water. What is 
the weight of the cork? 

6. A man weighs 150 lb. in air and 1 lb. in water. 
What is his specific gravity? 

7. An overturned boat will support more persons in 
the water than it will carry. Why? 

8. A lamp has a short wick. The oil may all be 
burned out. How? State the principle. 

9. The specific gravity of cork is .24. How much 
lead must be placed upon a cu. ft. of cork to sink it? 

10. A lighter 30 ft. wide and 50 ft. long and in the 
form of a box draws 3J ft. of water when loaded and 1 ft. 
when empty. What is the weight of its load? 


60 


HYDRAULICS. 


CHAPTER XIV. 

HYDRAULICS. 

1. Definition. 

2. Flow through pipes, a) velocity—law—formulae, b) 

quantity discharged, c) bursting pressure. 

3. Flow through orifices, a) head, b) velocity, c) quantity 

discharged, d) orifice of greatest range. 

4. Water wheels, a) Barker’s mill, b) turbine. 

PROBLEMS. 

1. In laying water mains right angles are avoided. 
Why? 

2. A reservoir is 150 ft. above the river. One pipe is 
used for its supply by a pump and for distribution there¬ 
from to the city. Can the pump w r ork and the city be 
supplied at the same time? Explain. 

3. How long will it take to empty a cubical tank 
which is 5 ft. on edge (inside), from a hole 1 in. in diam¬ 
eter in its bottom? 

4. Explain the Tantalus cup. 

5. What is meant by the Holly system of w r ater press^ 
ure? 

6. Give the reasons for the noise made by closing 
suddenly the faucet when the water is running. 

7. Does water flowing freely through a vertical pipe 
exert any lateral pressure? Why? Show by diagram. 

8. Water spouts from an orifice with a velocity of 
80.4 ft. per second. What is the head? 

9. A faucet f in. in diameter is left open. How many 
gallons of water is discharged in one hour with a constant 
head of 60 ft. ? 


HEAT. 


61 


10. What five hindrances to the flow of water through 
and out of pipes? 


CHAPTER XV. 

HEAT. 

1. Definition. 

2. Temperature, a) thermometers, b) graduation, c) ther¬ 

mometric scales, d) rules for changing readings, 
e) absolute zero of temperature. 

3. Expansion, a) in solids, b) in liquids, c) in gases, d) 

proofs of each. 

4. Liquefaction, a) effect on temperature, b) laws of 

fusion. 

5. Vaporization—effect on heat. 

6. Ebullition, a) laws, b) effect of pressure on boiling 

point, c) culinary paradox. 

7. Distillation, a) liquids, b) solutions. 

8. Latent Heat, a) of fusion, b) of solutions. 

9. Freezing Mixtures—dee machines. 

10. Solidification, a) change of bulk, b) liberation of heat. 

11. Condensation of gases—heat equivalents. 

12. Specific Heat—how determined. 

13. Conduction, a) in solids, b) in liquids, c) in gases. 

14. Convection. 

15. Radiation, a) in vacuum, b) in straight lines, c) in 

all directions, d) dependence, e) distance. 

16. Diathermancy. 

17. Absorption. 

18. Reflection, a) by mirrors, b) law. 

19. Refraction. 

20. Steam Engine, a) single acting, b) double acting, 

c) eccentric, d) governor, e) safety valve, f) con¬ 
densing engine, g) non-condensing engine, h) heat 
and work of engines. 


62 


SOUND. 


CHAPTER XVI. 

SOUND. 


1 . 


2 . 


3. 

4. 

5. 

6 . 

7. 

8 . 
9. 

10 . 

11 . 

12 . 

13. 

14. 

15. 


Definition, subjectively and objectively considered— 
illustrations. 

Waves, a) causes, b) lines of propagation, c) relation 
of waves to lines of propagation, d) period, e) 
length, f) amplitude, g) relation to velocity. 

Conditions, a) vibrating body, b) transmitting medi¬ 
ums, c) an ear to hear. 

Velocity, a) in air, b) in other media. 

Noise—music—scale, relation of its tones. 

Pitch, a) its dependence, b) proof. 

Intensity, a) effect of distance, b) law. 

Transmission—speaking tubes—toy telephones.. 

Reflection, a) experiments, b) echo. 

Telephone, a) action of, b) transmitter, c) receiver. 

Phonograph. 

Sympathetic vibrations. 

Interference. 

Beats—capacity of human ear. 

Laws of vibration of strings. 


16. Tones, a) fundamental, b) overtones, c) quality or 

timbre, d) simple, e) compound. 

17. Musical Instruments, a) wind, b) stringed. 

18. Define and describe: drum, violin, piano, accordion, 

Jew’s harp, guitar, melodeon, calliope, cornet, bu¬ 
gle, bag-pipe, dulcimer, flute, piccolo, cymbal, 
whistle, banjo, harp, tambourine, gong, castanets, 
lute, organ. 


LIGHT. 


63 


CHAPTER XVII. 

LIGHT. 

1. Definition. 

2. Medium, a) what, b) where existent. 

3. Relation of bodies to the ether, a) luminous, b) non- 

luminous. 

4. Transmission, a) manner—in straight lines, waves— 

line of propagation—wave-length—amplitude—re¬ 
lation to line of propagation, b) relation of bodies to 
transmission — transparent — translucent—opaque, 
c) forms in transmission—rays, three kinds—beams 

_pencils, d) velocity in transmission—rate—how, 

when, by whom discovered. 

o. Effects, a) what bodies are seen—the human eye—vis¬ 
ual angle, how increased and decreased—failure of 
the eye to reveal directly, size and distance of 
objects, b) in coloring of plants, c) inverted images 
from crossing of rays, d) shadows, definition—um¬ 
bra—-penunibra, e) in photography, f) invisibility 
of light. 

6. Intensity, a) how measured, b) effect of distance, 

c) law of squares. 

7. Reflection, a) definition, b) laws, c) apparent direction 

of visible bodies—cone of rays—intersection of 
two rays, d) mirrors—definition—plane—concave, 
principal axis, principal focus, center of curvature, 
secondary axes, conjugate foci — convex mirror, 
e) effects, a) real images, b) virtual images—con¬ 
struction of virtual image in plane mirror—in three 


64 


LIGHT. 


possible positions in concave and convex mirrors— 
construction for real images in concave mirrors— 
object in three different positions. 

8. Refraction, a) definition, b) laws, c) explanation, 

d) index of refraction, e) critical angle, f) total 
reflection, g) refractors—three kinds, h) lenses—six 
kinds—in any lens—principal axis—center of curv¬ 
ature—optical center and how located—conjugate 
foci, i) effects—real images, magnified and dimin¬ 
ished—virtual images, including definition, j) dia¬ 
grams showing construction for images in each 
kind of lens, each accurately made and explained, 
k) spherical aberration—how corrected—the Cod- 
dington lens. 

9. Chromatics, a) dispersion, definition—solar spectrum 

—pure spectrum—order of colors—Fraunhofer’s 
lines, b) composition of white light, c) color of 
bodies, d) the rainbow—conditions—dispersion in 
a raindrop—reasons for—diagram of bow—second¬ 
ary bow — reasons for its position—diagram, e) 
chromatic aberration—achromatic lens, f) interfer¬ 
ence, g) diffraction, h) irradiation, i) actinic rays, 
j) radiation and absorption—relation of one to the 
other, k) the electric light in photography. 

10. Polarization, a) definition, b) planes of vibration, 

c) polarization by absorption—tourmaline plates, 

d) polarization by reflection—angle for different 
substances — polariscope — its essential parts — ex¬ 
planation, e) polarization by double refraction— 
—double refracting substances—Nichol’s prism— 
what it is and how made—why so made. 

11. Optical Instruments, a) simple microscope—kind of 

lens — why achromatic — provision for spherical 


LIGHT. 


65 


aberration—position of the object—kind of image 
—accurate diagram of lens, object, rays and image, 
b) compound microscope—monocular—binocular— 
stand—stage—mirror—objective, eye-piece, appa¬ 
ratus for focusing—diagram presenting sectional 
view of all parts of the compound microscope, also 
showing object, path of rays, and image, c) tele¬ 
scope—refracting—the refractor—eye-piece—loca¬ 
tion of several such telescopes—reflecting telescopes 
—name and location of one, d) opera glass—dia¬ 
gram presenting a sectional view of instrument and 
showing, also, object, path of rays, and image— 
explanation of same, e) stereoscope, a) how lenses 
are placed—diagram with explanation—manner of 
taking photographs for stereoscope, f) magic lan¬ 
tern, g) solar camera, h) kaleidoscope, i) common 
spectacles — give accurate diagrams presenting a 
sectional view of lens and human eye, showing also 
object, path of rays to the retina, and effect of 
lenses of different curvature. 


66 


MAGNETISM. 


CHAPTER XVIII. 

MAGNETISM. 

DEFINITION. Magnetism is electricity in rotation. 

This is shown by the way a magnet acts. 


i 

























MAGNETISM. 


67 


Tliat a magnet acts in this way may be seen by placing 
a magnet under a sheet of paper on which are some iron 
filings. 



MAGNET. The word magnet comes from Magnesia, 
a town in Asia Minor, where the lodestone was discovered. 

DEFINITION. A magnet is a mass of polarized molecules. 

By division and subdivision of a magnet, it is proven 
tnat each part, however small, is a magnet. 

Plunge a white hot watch spring into cold water. 
Magnetize it by rubbing it one way with a lodestone or a 
magnet. 

Break it in pieces. Each part shows polarity. 



Fig. 56. 


KINDS. Magnets are natural or artificial. Natural 
magnets are of meteoric origin. They are magnetic oxide 
of iron and are represented by Fe 3 0 4 . 















68 


MAGNETISM. 


SUSPENDED MAGNET. If a natural magnet be sus¬ 
pended as shown, it will point N. and S. 



Fig. 57. 


Fig. 58. 


REASON. All the molecules of the magnet being 
polarized face each way from the center. This polarity 
increases to points near its extremities. The influence of 
the earth as a magnet causes the north-seeking pole to turn 
to the N. magnetic pole of the earth—from the law: Like 
poles repel and unlike poles attract. 

From the above it appears that the magnetism of 
either pole is the opposite of that indicated by its sign. 

By balancing, find the axis of a croquet ball. Closely 
fit a f in. magnetized steel rod in a hole bored through 
the axis, the magnet terminating at the surfaces. 

If suspended with the magnet horizontal, the latter 








MAGNETISM. 


69 


will take position in a magnetic meridian of the earth and 
point N. and S. The ball now fairly represents the 
earth and its magnetic poles. 

With a natural or artificial magnet, magnetize by rub¬ 
bing one way only, a knitting needle. 

Suspend the needle over the globe in a position parallel 
to the enclosed magnet, and notice the position taken by it. 

This experiment illustrates the statement concerning 
the earth as a magnet. 

SIGNS ON MAGNETS. The north-seeking pole of a 
magnet may be marked N -(-, or with a notch. 

The south-seeking pole bears opposite signs or is un¬ 
marked. 

However marked, the magnetism of the pole is opposite to 
that indicated by its sign. 



Determine from the above figure the poles of a mag¬ 
netized knitting needle by testing with a common magnet. 

Mark the poles. 















70 


MAGNETISM. 


HOW TO MAKE A MAGNET. Take two bar magnets 
and use them as indicated in 


C 



Fig. 60. 


Draw the magnets from the center of the unmagnetized 
bar to its ends and carry them back to repeat the action. 

Do this a dozen times on opposite sides of the bar, 
terminating the last stroke at the center of the bar. 

Mark the poles and test as indicated in Fig. 59. 

II. Use a horseshoe magnet as indicated in 



Repeatedly draw the short piece of soft iron from the 
center of the magnet to the center of the bar. 

Make each stroke the same way. 

Without separating the poles of the magnets, invert 
them and repeat the strokes until the bar is saturated. 















MAGNETISM. 


71 


SATURATION. By saturation is meant that the mole¬ 
cules have received all the magnetism they can retain. 

RETENTIVITY. The retentivity of a magnet is its 
power to retain magnetism. 

The retentivity of iron is little, that of steel is great. 

Iron receives and parts with magnetism quickly. 

Steel magnetizes slowly and holds it. This is thought 
to be due to the fixedness of its molecules. 

The freedom of motion of the molecules in liquids 
prevents retentivity. 

Magnetize mercury. Upon the withdrawal of the 
magnetizing force its molecules rearrange themselves as 
before magnetization. 

DEPTH OF SATURATION. Not all the molecules of 
a magnet are saturated. Only a shell of such molecules 
exists. 

This may be proven by dissolving this outer coat with 
sulphuric acid, when the remaining bar is found to have 
no magnetism. 

For this reason a bar to be magnetized is turned over 
in the process. 

LOSS OF MAGNETISM. Magnets lose their power in 
three ways: 

1. By unprotected poles. 

2. By blows or jars. 

3. By heat or cold. 

Treat magnets of your own make in the above ways 
for proof. 

HOW TO KEEP A MAGNET. For a bar magnet place 
a piece of soft iron on each pole. 

For a horseshoe magnet cover both poles with a short 
bar of soft iron called an armature. 


72 


MAGNETISM. 


An armature completes the magnetic circuit and pre¬ 
vents loss of magnetism. Such an armature is temporarily 
magnetized, each end having opposite magnetism to the 
pole it joins. 

Not only may the power of a magnet be retained, but 
its power may be increased. 



Fig. 62. 


Load the can as shown with all the nails the magnet 
can support. Each day add more. In this way Sir Isaac 
Newton caused a magnet to support two hundred times its 
own weight. 







MAGNETISM. 


73 


Carefully remove the load. The magnet loses its in¬ 
creased magnetism, returning to its former condition. 
This is thought to be due to a change in the position of 
the molecules assumed by them upon the removal of the 
strain. 

LINES OF FORCE. The lines of force are lines along 
which the magnetism acts. 

These are curved lines extending from pole to pole, 
and on all sides of the magnet. Those nearer the magnet 
form closed circuits. 



Fig 63. 

This may be shown by experiment. Plunge a round 
bar magnet into iron filings of varying degrees of fineness. 
They assume positions in the lines of force. 


I 



Fig. 64. 


MAGNETIC FIELD. The magnetic field of a magnet 
is the space through which the lines of force pass. 

The magnetism in this field is strongest nearest the 
magnet. 







74 


MAGNETISM. 



Fig. 65. 


Hence the following laws: 

I. Magnetism decreases as the square of the distance from 
the poles increases. 

II. The force between any two magnetic poles is equal to 



















MAGNETISM. 


75 


the product of the numbers representing their strengths divided 
by the number representing the distance between them. 

SELECTIVE POWER. If a magnet be applied to a 
mass of brass and iron filings, mingled with sand and saw¬ 
dust, it will select the iron only. 

A MAGNETIC BODY. A magnetic body is one that is 
attracted by a magnet. Paper, pith and cotton are feebly 
magnetic under the influence of a powerful magnet. 

LIFTING POWER. The lifting power of a magnet de¬ 
pends upon: 

1. Its form. 

2. Its strength. 

A horseshoe magnet will lift twice as much as a bar 
magnet of the same size and strength because the magnet¬ 
ism of both poles acts upon the weight at the same time. 

FORM OF MAGNET. The form of a magnet has ref¬ 
erence to: 

1. Its general shape. 

2. The shape of its ends. 

GENERAL SHAPE. The most common form is that of 
a horseshoe, because of its convenience, lifting power, and 
use of single armature or keeper. 

SHAPE OF ENDS. Common magnets are flat, with a 
thickness varying from to of the width. 

This form coincides best with the form of the ideal 
magnet, which is a bar so thin that all of its molecules 
are polarized. 

STRENGTH. The strength of a magnet is the force 
exerted by one of its poles. 

From this it appears that the lifting power of a magnet 
is not less than twice its strength. 


76 


MAGNETISM. 



Fig. 66. 





Fig. 67. 


FACTS. 1. Magnetism and electricity are identical. 
Mendenhall in “A Century of Electricity,” p. 75. 

2. Magnetism may be hastened or lost by jars or tor¬ 
sion. Atkinson in “Dynamic Electricity,” p. 54. 

3. Magnetism is strongest at the poles and nil at the 
center. Silliman in “ Principles of Physics,” p. 510. 

4. A piece of steel magnetized and demagnetized is 
not in the same condition as at first. Lodge in “ Modern 
Views of Electricity,” p. 162. 

5. Magnetism cannot be insulated. “ Modern Views of 
Electricity,” p. 152. 

6. Magnetized spheres and circular disks have no dis¬ 
tinguishable poles. “Dynamic Electricity,” p. 63. 













MAGNETISM. 


77 


CAUTIONS. 1. A magnet should be kept, poles down¬ 
ward, in the magnetic meridian. 

2. The poles should be covered with an armature, 
which should be placed on and taken off with a gentle, 
sliding motion. 

3. Do not handle a magnet rudely. Avoid jars or 
shocks caused by dropping or by blows. 

4. Do not subject a magnet to extremes of heat or cold. 

THEORIES. The oldest theory supposes that all bodies 

are permeated by two electrical fluids, which are mutually 
attractive and repellent. 

Combined they are neutral. Magnetization separates 
these fluids. (Franklin.) 

A later theory supposes that each molecule of a mag¬ 
netic body has a current of electricity circulating around 
it, thus: 



Fig. 68. 


(Ampere.) 


78 


MAGNETISM. 


These currents before magnetization circulate in different 
directions, owing to the positions of the molecules, and 
there is produced, therefore, no external effect. 

After magnetization these currents circulate in the same 
relative direction and the molecules now face about and 
look along the lines of force. 



The act of magnetization consists in changing the 
positions of the molecules so that the effect of their com¬ 
bined magnetism is manifested by the bar as a whole. 

Magnetization adds no magnetic force to a body. 

SUPERSTITION. Pliny believed that the word magnet 
was derived from Magnes, a herdsman who found himself 
held to a magnetic rock by the nails in his shoes and the 
iron in his staff. 


INDUCTION. 


79 


The ancients used magnets to suspend statues in their 
temples to awe the worshippers. 

Mahomet’s coffin ‘‘soared” in a sanctuary of magnetic 
stones. 

It is a popular belief in Japan that magnets lose their 
power just before earthquakes. 

Magnets are credited with medicinal and revealing 
powers, such as curing diseases and revealing secrets. 

Superstition claims that a magnet may reveal the 
motives of a bride in the choice of her husband. 

Superstitious notions of the form and attractive power 
of the magnet have survived the past. 

Good luck is believed to come to that American home 
whose walls are decorated with the object, the image, or 
the picture even, of a horseshoe. 


CHAPTER XIX. 

INDUCTION. 

In the foregoing work on magnetism, induction has 
been implied in all the theory and has formed the basis 
for nearly all of the work. 

Topics are so closely related in science work that no 
one of them can be fully treated alone. 

DEFINITION. Induction is the process of developing 
magnetic or electric phenomena through the agency of lines of 
force. 

If a body is magnetized or electrified by induction, it 
is because of its proximity to a magnet or a current. 

That magnetism and electricity are identical, may be 


80 


INDUCED MAGNETISM. 


shown by suspending a magnetized knitting needle as in 



Place a wire joining the two poles of a battery under 
or over and parallel to the needle. 

It instantly turns to a position at right angles to the 
wire. 

Since magnetism is electricity in rotation, and since a 
current of electricity is brought parallel to a freely moving 
mass of polarized molecules, the position of the magnet is 
what we should expect. 

Oersted’s experiment before his class. “A Century 
of Electricity,” p. 76. 

CHAPTER XX’ 

INDUCED MAGNETISM. 

Bring one pole of a magnet into contact with a piece 
of soft iron and this into contact with some iron filings. 



Fig. 71 , 









INDUCED MAGNETISM. 


81 


Hold the iron a short distance from the magnet as 
indicated in 


Fig. 72. 


I 

th 


Arrange a magnet, bar and needle as indicated in 


A/ $ 

T T 

Fig. 73. 

Portative magnetism. 




TERRESTRIAL MAGNETISM. Suspend a magnetized 
bar from its center in a room free as possible from iron or 
steel and free from air currents. Allow the bar to come 
to rest. It points to the north magnetic pole of the earth, 













82 


INDUCED MAGNETISM. 


and by its position indicates a magnetic meridian of the 
earth. 

MAGNETIC MERIDIAN. A magnetic meridian is a me¬ 
ridian whose position is indicated by a line of force extending 
through the magnetic poles. 

What does the needle of a pocket compass indicate by 
its position when it is at rest? 

VARIATION. The croquet ball. On the croquet ball 
represented in Fig. 67a, establish a point representing the 
earth’s north geographical pole from the following: 

1. Let the north-seeking pole of the enclosed magnet 
represent the north magnetic pole of the earth. 

2. The north magnetic pole of the earth is in about 
70° north latitude. 

From this it appears that the north magnetic pole of 
the earth is about 20° south of its north geographical pole. 
The position of the south magnetic pole has not been 
accurately determined. 

Next establish a line representing the earth’s equator 
and a point representing its south pole. 

Draw several lines extending from pole to pole rep¬ 
resenting geographical meridians, one of which passes 
through the geographical and magnetic poles. The ball 
now represents the earth. 

On the ball select a meridian which does not pass through 
the magnetic poles. 

On the meridian select a point north of the equator. 

On this point place a pocket compass with the center 
of its needle directly over it. 

Allow 7 the needle to come to rest. It indicates the 
position of a magnetic meridian. 

The angle formed at the point selected by the inter¬ 
section of the tw r o meridians is the angle of variation for 
that point. 


INDUCED MAGNETISM. 


83 


If the center of the needle be moved along the geo¬ 
graphical meridian toward the north pole it will be seen 
that the angle of variation increases. Why? 

Place the compass on a point in the meridian which 
passes through both poles. Explain the result. 

In a similar manner, place the compass on different 
meridians, noticing that the needle points east or west of 
the north geographical pole. 

Would the needle point east or west of the true north 
if placed on the meridian passing through the place of 
your residence? How much? Approximately measure 
this variation in degrees. 


at 



Fig. 75. 


84 


INDUCED MAGNETISM. 


In 1890, the variation for San Francisco was 16° 34' E. 

DIP OF THE NEEDLE. Suspend and balance a small 
magnetized darning needle. When it is at rest bring the 
north magnetic pole of the ball under the point of sus¬ 
pension. 

The needle takes a vertical position. 



When the magnet is in a horizontal position the needle 
is nearly so and tangent to the ball at its equator. 

Turn the ball so that the needle may come under the 
direct influence of the south magnetic pole. 














INDUCED MAGNETISM. 


85 




(N. and S. on the needle indicate north and south 
seeking poles.) 

Leave the needle suspended in a closed room, free 
from iron and steel, during the night. In the morning, 
notice its dip. 

The dip of the needle for San Francisco in 1885 was 
62° 15'. 

Of w T hat value to the surveyor and mariner is a knowl¬ 
edge of the variation of the needle, or its dip? 

The illustration of the ball and needle has been given 
for the reason that it points along divergent and inter¬ 
minable, though interesting, lines of thought which the 
wise teacher must judge when and where to cut off. 








86 


ELECTRICITY. 


CHAPTER XXI. 

ELECTRICITY. 

DEFINITION. Give the etymology of the word. 

Just what electricity is, is still unknown. 

By many, it is believed to be a form of energy; others 
claim that it is a mode of molecular motion. 

Our most advanced thinkers incline to the belief that 
it is a substance. 

More will be said about this further on. 

Our best way is to play with it. 

EXPERIMENTS. There exists a notion that simple 
experiments should be discarded. They should be en¬ 
couraged, rather. 

No topic in science presents phenomena so wonderful 
and through the use of apparatus so simple as electricity. 

It is hoped that teacher and pupil will multiply illus¬ 
trations until the principle stated is fully understood. 

In all experimentation, one thing suggests another, 
and this inquiry on the part of the pupil for more light 
and new proof is investigation. 

FRICTIONAL ELECTRICITY. Frictional electricity is 
electricity developed by mechanical excitation. 

Its phenomena are classed under attraction and repul¬ 
sion. 

ATTRACTION. Rub a vulcanite ruler or rod with a 
flannel. Bring it near a lead pencil suspended as indi¬ 
cated in 


ELECTRICITY. 


87 



In like manner approach the pencil with a stick of 
sealing wax, a roll of sulphur or a glass rod after rubbing 
each with a dry flannel. 

Apply the same electrified bodies to bits of paper, pith 
or feather clippings. Why are these attracted? 

All bodies have electricity and are conductors or non¬ 
conductors of it. 

The terms electrics and non-electrics are evidently 
inapplicable. 

ELECTRIFIED BODIES. An electrified body is one 
that manifests electricity. 

EXCITANTS. That which is used as a rubber is called 
an excitant. 

Repeat these experiments, using the excitants as elec¬ 
trified bodies. What happens? 

Bring an electrified glass rod near bits of paper, as 
indicated in 








88 


ELECTRICITY. 



What happens to such bits as touch the glass? Why? 
State the law of attraction and repulsion. 

Split a lath lengthwise and suspend one half as indi¬ 
cated in 



Fig. 81. 

















ELECTRICITY. 


89 


This lath, as adjusted, may be made to show attraction 
and repulsion. How? 

From the above experiments it appears that unlike 
substances undergoing the same act have manifested forces 
of equal strength and opposite in character. 

Shall we say that the act has developed positive and 
negative electricities? Perhaps not. 

The terms positive and negative imply a standard of 
comparison. 

STANDARD. What is the standard? 

All electricians refer to the electric condition of the 
earth for a standard of comparison. 

This electric condition of the earth is rated zero. 

Bodies having the.same electric condition as the earth 
are without electric potential. 

Such bodies as are in a higher electric condition have 
positive potential. Those lower, negative potential. 

Electric potential is the difference in the electric conditions 
of two bodies compared. This difference may be one of 
intensity or quantity. 

The electric condition of a body may be referred to 
that of another, or to that of the earth. 

Experiments in Static Electricity ignore the electric 
condition of the earth except as communication with it 
favors or hinders the experiments. 

ATTRACTION AND REPULSION. Attraction and re¬ 
pulsion are but manifestations of states of potential. 

Bodies of like potential repel and those of unlike 
potential attract. 

These statements do not explain attraction and repul¬ 
sion. 

Just why electricity, in passing from a body of a 
higher potential to one of lower, causes attraction, or why 


90 


THE ELECTROSCOPE. 


two equally electrified bodies cause, upon their approach, 
repulsion, is something that future investigation will shed 
more light upon. 

Modern writers incline to believe with Franklin, that 
there is one kind of electricity, and that all electric phe¬ 
nomena are the result of having taken it from one body 
and put it into another. 

Let us try another experiment. 


CHAPTER XXII. 

THE ELECTROSCOPE. 

First prepare a gold leaf electroscope with which to 
test electric potential. 

Thoroughly dry a quart bottle and hang a strip of 
gold leaf on a brass rod as indicated in 



Fig. 82. 











THE ELECTROSCOPE. 


91 


CAUTIONS, a) The stopper of the bottle should be 
of insulating material, b) The leaves should not be long 
enough to reach the sides of the bottle. 

With the bodies and excitants already used, test the 
relative kinds of potential. 

Higher relative potential is positive, and is indicated 
by the sign -|-. 

Lower relative potential is negative, and is indicated 
by the sign —. 

AN ELECTROSCOPE SHOWS: 

1. The presence of electricity. 

2. Its relative amount. 

It will be found on further use of the instrument that 
different degrees of the same potential increase or decrease 
the divergence of its leaves. 

From this it appears that the electroscope does not 
reveal the potential of a body with respect to that of the 
earth. 

It only shows the amount that one body has when com¬ 
pared with that of another. 

The electroscope proper is the disk, the rod, and the 
suspended leaves. 

The bottle is simply for protection and support of the 
electroscope. 

If the electroscope be put in direct communication 
with the earth and its disk be approached by any electri¬ 
fied body, its leaves diverge. 

In this case, electricity passes to or from the earth, 
causing the divergence of the leaves. 

The direction which it takes is the true test of electric 
potential. 


92 


THE ELECTROSCOPE. 


Now try the following experiment: Fit a flannel cap 
over a vulcanite rod as indicated in 



Twist the rod in the cap and remove it with the silk 
thread. Bring the cap by its thread near the disk of the 
electroscope to test its potential. 

Notice divergence. 

Bring the rod near the disk. 

Notice convergence. 

The rod is negatively charged with respect to the 
flannel. 

The same act has developed potentials of opposite 
characters. 

Shall we say opposite electricities? 

Will it not be more consistent to say opposite poten¬ 
tials, and attribute the phenomena to the difference in 
degree of electrification of the bodies used, due to their 
difference in constitution? 

This is the belief of Mr. Atkinson, whose recent works 
on electricity are attracting much attention. 

Let us now represent the cap folded and the rod cut 
off to the same length as indicated in 


THE ELECTROSCOPE. 


93 



Fig. 84. 


Lines of force may be considered as existing between 
the two bodies, as was shown in the magnet. 

Upon the wider separation of these bodies the repre¬ 
sentation would be as indicated in 



A line of force is a line along which electricity passes from 

























94 


THE ELECTROSCOPE. 


a point of higher to one of lower potential. (See experiment 
illustrating this under Galvanic Electricity.) 

Insulate a lead pencil and join its lead to the electro¬ 
scope, as indicated in 



Approach the exposed lead with a body of negative 
potential. 

The result is indicated in the drawing. 

The lead of the pencil has conducted the electricity to 
the electroscope. 

CONDUCTOR. A conductor is a body that favors the 
transfer of electricity. 

If the experiment be repeated with a short stick and 
the connections made as before, the experiment will fail. 

The wood of the stick offers resistance to the transfer 
of electricity, or is a non-conductor of it. 

NON-CONDUCTOR. A non-conductor is a body which 
offers high resistance to the transfer of electricity. 

The best conductors are silver, copper, iron, and zinc. 

The poorest conductors are vulcanite, rubber, glass, 
wood and paper. 

The standard of conductivily is that of silver. It is 












THE ELECTROSCOPE. 


95 


rated at 100. Copper is then rated at 73, brass at 22, 
iron at 13. 

Copper, iron, and brass are the most important metals 
used in the practical application of electricity. 

For additional experiments with the electroscope, see 
Poyser in “Magnetism and Electricity.” 

For the more complete mastery of this instrument, see 
Atkinson in “Static Electricity.” 

CAUTIONS. The two most important cautions in the 
foregoing experiments are those regarding temperature 
and insulation. 

The bodies used and the surrounding air must be dry. 

Rubber corks, shellac, vulcanite, and paper are the 
experimenter’s friends in this work. 

The open secret in all successful experimentation in 
frictional electricity is insulation. 

INSULATORS. An insulator is a non-conductor used to 
confine electricity within certain limits. 

The value of insulation cannot be overestimated in all 
successful work with electricity. 

Along the line of effort to bring electricity to practical 
uses, perhaps no topic concerning it has been more thor¬ 
oughly investigated or more successfully mastered than 
this one of insulation. 

In fact, each pupil should be on his guard in every 
electric experiment lest this subtle force escape his grasp. 

We are not to forget that the best insulator is a feeble 
conductor. 

Oftentimes the apparent behavior of electricity is due 
to an oversight of the fact that while the air is a universal 
insulator, it is also a conductor and may manifest all 
kinds and many degrees of potential. 


96 


THE ELECTROPHORUS. 


Further investigation may prove to what extent the 
divergence of the leaves of the gold leaf electroscope may 
be due to the surrounding air and glass. 

Who has tried the action of an electroscope in a 
vacuum? 


CHAPTER XXIII. 

THE ELECTROPHORUS. 

Give the etymology of the word and explain its 
meaning. 

DEFINITION. An electrophorus is a miniature electric 
machine for obtaining a difference of electric potential. 

The student should make one. 



Fig. 87. 

Directions for making an electrophorus: 

BASE. From dry wood make a base 12 in. square and 
1 in. thick, which will not warp. Cut a sheet of tin and 
one of thin vulcanite the same size. At the middle point 
of one side of the tin, solder a piece of brass \ in. wide 
and 1 in. long. 

Fasten both sheets, with the brass beneath, to the base. 
Bend the narrow strip of brass over the upper side of the 
vulcanite and extending inward from its edge $ inch. 
















TIIE ELECTROPHORUS. 


97 


COVER. The cover is a circular piece of No. 20 brass 
10^ inches in diameter, having a wire carefully soldered 
to the edge of its upper surface. 

A vulcanite handle 7 in. long is fastened to its center 
by soldering one-half of a f in. gas pipe connection to the 
brass, and screwing the vulcanite into it. 

A small brass or other metal ball is fastened to the 
cover, as indicated in the figure. 

USE. Upon beating or rubbing the vulcanite plate 
with a catskin or a flannel rag, it becomes electrified. 

Place the cover on the plate. Bring its edge against 
the end of the brass strip. 

Remove the cover and use it as indicated in 




Fig. 88. 


EXPLANATION. The plate having been charged neg¬ 
atively by the excitation, a like amount of electricity is 
attracted from the earth to the under side of the plate and 
to the upper surface of the brass plate under it, both 
surfaces being charged positively by induction. 







98 


THE ELECTRIC MACHINE. 


The under surface of the cover becomes positive and 
its upper surface negative. 

Test these surfaces by a proof plane, shown in 



Fig. 89. 


The proof plane is made of brass, with an insulating 
handle. 

When the edge of the cover was brought against the 
end of the brass strip, the accumulated electricity of the 
lower plate passed to the cover. 

The cover becomes positive. 

Its charge is bound to the plate while in contact with it. 

Upon removal of the cover and applying the knuckle 
as indicated, a spark is obtained about \ inch long. 

The electrophorus is of great value to the pupil in 
aiding to an insight into various processes of induction 
and accumulation of electricity. 

If made and used correctly, it is sure to work. 


CHAPTER XXIV. 

THE ELECTRIC MACHINE 

DEFINITION. An electric machine is an instrument for 
developing and accumulating electricity by friction. 

No cut or description of it is given. 

An electric machine is too difficult for a pupil to make. 
But he should learn to use it and to explain the general 
principles of its action. 




THE ELECTRIC MACHINE. 


99 


In all such machines metal brushes are used to develop 
electricity. * 

This fact is a strong argument in support of the state¬ 
ment that electricity resides in all bodies. Why? 

The following are some of the principles concerning 
the action of the Toepler-Holtz Machine. 

PRINCIPLES. I. A Toepler-Holtz Machine is self¬ 
charging and self-sustaining. 

II. By a series of inductions electric potential is in¬ 
creased. 

III. By conductors and insulators the electricity is led 
along to the accumulators or Leyden jars. 

IV. The electrodes from these jars lead electricity of 
high, but opposite, potentials, toward each other to form 
the electric spark. 

V. The sources of electricity are the earth, air, and 
the machine itself. 

The full explanation of the electric machine will be 
possible to that pupil who can recall, apply, and extend 
the processes of the electrophorus, adding, of course, the 
explanation of the Leyden jar, which will now be given. 

LEYDEN JAR. Explain the word and give its history. 
See Silliman in “Principles of Physics,” p. 558. 

HOW TO MAKE A LEYDEN JAR. Select a wide¬ 
mouthed half gallon jar of bright green glass. 

Candy jars are not good for this purpose because of 
the conductivity of the glass. 

Coat the entire inside and outside of the jar with tin- 
foil three-fourths of its height. 

The coating is best put on with paste. 

Leave no open surfaces. 

Fit a cover of baked wood to the top of the jar. 


100 


THE ELECTRIC MACHINE. 


Through this put a brass rod, having a ball on its top 
and a short brass chain attached to its lower end and 
reaching to the bottom of the jar. 

Varnish inside and out all uncovered surfaces. 

DEFINITION. A Leyden jar is an accumulator of 
electricity. 



CHARGING THE LEYDEN JAR. To charge the jar, 
place either the inner or outer coating in connection with 
the prime conductor of the electric machine. 

The other coating is to be connected in a convenient 
way to the earth. 

The jar may be charged negatively from the negative 
electrode. 

With the connections made as described and the elec¬ 
trodes of the machine well separated, turn its plate until 
the jar is “ full.” 

USE. The jar with its charge may now be taken with 
both hands to any experiment to be made. 





















101 


THE ELECTRIC MACHINE. 

The electricity is to be led through the experiment by 
a discharger. 



Fig. 91. 


To discharge the jar, place one knob of the discharger 
to the outer coating and bring the other to the knob of 
the jar. 

EXPERIMENTS. To use the charge of the jar, place 
the experiment between the outer coating of the jar and 
its knob by means of conductors that lead through the 
discharger. 

EXPLANATION. The jar is charged positively on its 
outer coat by holding its knob to the prime conductor of 
the machine. 

This charge repels electricity to the outer coating, 
which should be in connection with the earth or the nega¬ 
tive electrode. 

Electricity may be accumulated to such a high degree 
of potential that the jar may be broken. 

For charging the jar negatively, reverse the conditions. 

The following typical experiments are stated and illus¬ 
trated, hoping that the pupil will classify them under the 
following heads of 



102 


STATIC ELECTRICITY. 


CHAPTER XXV. 

STATIC ELECTRICITY. 

EFFECTS. 

1. Attraction. 

2. Repulsion. 

3. Physiological. 

4. Mechanical. 

5. Chemical. 

6. Luminous. 

7. Magnetizing. 

DEFINITION OF STATIC ELECTRICITY. Give the 

etymology of the word static. 

Static Electricity is electricity at rest. 

It resides only upon the surface of bodies. 

TYPICAL EXPERIMENTS. Place a pupil upon an 
insulating stool as indicated in 



With the machine charge the pupil. 

Draw sparks from this pupil. 

Have the pupil place his hand over bits of cotton or 
over the dry hair of another pupil. 






STATIC ELECTRICITY. 


103 


Present to the knuckle of this pupil one end of the 
balanced lath represented in Fig. 81. 

By use of the machine, pass electricity through a piece 
of insulated tin-foil that supports a common knitting 
needle, as indicated in 



Draw a spark from the prime conductor as indicated in 



Write on a pane of glass with a sharpened stick 
dipped in thin glue. With care sprinkle iron filings on 











104 


STATIC ELECTRICITY. 



the tracings. Observe the connections and breaks in the 
writing. 



Fig. 95. 

Support in a funnel fine dry sand. Connect to the 
electrodes of the electric machine. 



Fig. 96. 









































STATIC ELECTRICITY. 


105 


Fill a eudiometer with water and invert it over a 
shallow dish of water. 

Pass into the eudiometer oxygen enough to cover the 
platinum wires. 

Add twice as much hydrogen as oxygen. 

Hold the tube firmly in position and pass the spark 
through the wires. 


fh 



Fig. 97. 


Pass a spark through a dozen pieces of sized paper 
and notice how many pieces have the double burr. 






106 


STATIC ELECTRICITY. 



ELECTRIC DISCHARGE. 

DEFINITION. The electric discharge is the neutralization 
of positive and negative potentials. 

The discharge may be silent or take the form of 

1. The spark. 

2. The brush. 

SILENT DISCHARGE. Silent discharge is the unob¬ 
served escape of electricity to surrounding bodies. 

The experimenter is cautioned to be guarded on this 
point. 

THE SPARK. The spark is incandescent matter having 
a vibratory motion of inconceivable velocity. 

It may be spread out as in the illuminated pane, or 
form a succession of disks in Geissler Tubes, or be length¬ 
ened to several miles, as in lightning. 

For the shape, color, length and duration of the spark, 
see Deschanel’s Philosophy, p. 583. 

THE BRUSH. The brush is a multitude of glowing 
lines of matter radiating from charged convex surfaces. 

St. Elmo’s Fire is a form of brush discharge. 

The brush from the positive electrode is much finer 
than that from the negative. 











ATMOSPHERIC ELECTRICITY. 


107 


EFFECT OF POINTS. Electricity is rapidly discharged 
from points and thin edges. 

In the electric machine points are used to take up 
electricity from a charged body. 

In ordinary experimentation, points and sharp edges 
are to be guarded against to prevent the escape of elec¬ 
tricity. 


CHAPTER XXVI. 

ATMOSPHERIC ELECTRICITY. 

The atmosphere, with the earth’s surface, forms an 
immense Leyden jar. 

The upper strata form the inner coating, the lower the 
insulating medium, and the surface of the earth the outer 
coating. 

We move upon this outer coating and are thus enabled 
to see much of the electric phenomena above us. 

This topic may be studied under the following points: 

I. Causes. 

1. Temperature. 

2. Conditions of vegetation. 

3. Resistance of air strata. 

4. Clouds. 

5. Winds. 

II. Lightning. 

1. Definition. 

2. Kinds. 

a. Forked. 

b. Sheet. 

c. Globular. 

3. Direction. 

a. To the earth. 


108 


ATMOSPHERIC ELECTRICITY. 


b. From the earth. 

4. Length. 

5. Velocity. 

6. Effects. 

a. Disruptive. 

b. Heating. 

7. Rods. 

III. Thunder. 

1. Definition. 

2. Clap. 

3. Rumble. 

4. Rattle. 

5. Return shock. 

For a mastery of the above outline, consult “Static 
Electricity,” chap. xii. Atkinson. 

ELECTRIC INDUCTION. 

Give the etymology of the word. 

Those best acquainted with electricity are unable to 
say what induction is. 

This follows from the fact that scientific men have 
not yet agreed upon a definition of electricity. 

Electric induction may be defined in a general way, as 
a process of developing electric phenomena by the ap¬ 
proach of two unequally electrified bodies separated by an 
insulator. 

All the experiments performed in Magnetism and 
Frictional Electricity have resulted from inductive pro¬ 
cesses. 

INDUCTIVE EFFECTS. In the use of the electroscope 
the inductive effect of the electrified body was greatest 
when near the disk and least when far from it. 


ATMOSPHERIC ELECTRICITY. 109 

The difference in divergence of the leaves showed, 
approximately, degrees of inductive effect. 

An electrometer shows this effect to vary in a con¬ 
stant ratio, thus establishing the law: 

Electric induction varies inversely as the square of the 
distance. 

INFLUENCE OF INSULATORS. Inductive effects are 
also influenced by the properties and arrangement of the 
molecules of the insulator. 

Strain is produced upon these molecules by the pres¬ 
ence of an electrified body. 

This strain varies with the constitution of the insulator. 

The efficiency of an insulator increases as its molecules 
resist strain, thus preventing the escape of electricity. 

Hence the inductive capacity of an insulator may be 
measured. 

A standard for inductive capacity is that of air at 
32° F. and at a pressure of 29.92 inches of mercury. 

The inductive capacity of all insulators is measured by 
this standard. 

The ratio resulting from such a measurement is the 
specific inductive capacity of that body. 

The following table may help the pupil to a choice of 


an insulator. 

Dry air,.1. 

Paraffin, - - - - - - 2.09 

India rubber, - - - - 2.23 

Shellac,.2.65 

Glass (average), - - - - 5.87 

Petroleum,.2.05 


Instructive and valuable as are all experiments under 
frictional electricity, we are forced to admit that it plays 
a small part in the present practical applications of this 
subtle force. 


110 


DYNAMIC ELECTRICITY. 


CHAPTER XXVII. 

DYNAMIC ELECTRICITY. 

DEFINITION. Give the etymology of the word 
dynamic. 

Dynamic electricity is electricity in motion. 

It can exert power at great distances from its source. 
The former terms used were galvanic and voltaic. 
Why? 

Give a short sketch of the discoveries of Galvani and 
Volta. 

What was the frog experiment? 

Who performed it? 

You perform it. 

Pith the frog and then skin him and treat as in 



(Use narrow strips of copper and zinc.) Explain. 






DYNAMIC ELECTRICITY. 


Ill 


A GALVANIC BATTERY. 

DEFINITION. A galvanic battery is an apparatus for 
developing difference of potential by chemical action. 

It may consist of one or of many cells. 

A single cell is called an element, and is shown in 



AN ELEMENT. An element is a glass vessel containing 
an exciting fluid, usually acid, in which are placed two dis¬ 
similar metals. 

This element is a simple battery. 

CURRENT. Suppose the metals are zinc and copper 
and the acid dilute sulphuric. 

On joining the plates as shown, the zinc acts on the 
acid, but the copper does not. 

(While the action is mutual, it is agreed, in chemistry, 






112 


DYNAMIC ELECTRICITY. 


that the metals begin it and hence rank first in all state¬ 
ments.) 

This chemical action gives high potential at the zinc 
plate and a current of electricity is conducted by the 
liquid to the copper plate of lower potential. 

From this, we see the zinc plate is called positive in 
the liquid and the copper negative. 

In this action, water is decomposed and hydrogen 
bubbles appear at the copper plate and oxygen at the 
zinc plate. 

Copper being a good conductor, the high potential it 
has received is carried to the air end of the plate, which 
is now called positive and marked -f-. 

In accordance w r ith Franklin’s theory, stated elsewhere, 
electricity passes from a body of higher potential to one 
of lower, the former losing and the latter gaining. 

Hence the air end of the zinc plate is called negative 
and marked —. 

If the. plates are joined as shown in the figure, a com¬ 
plete circuit is formed and chemical action continues. 

But certain influences hinder the constant action of the 
battery, which will be considered under The Choice of 
Liquids. 

Why do the ends of the plates bear opposite signs? 

CURRENT. The term current is a misnomer. 

There is no current,—no flow,—no visible movement. 

Electric energy begins at a given point and is spent 
perhaps hundreds of miles away, a fractional part of a 
second being required for its transmission. 

The most suggestive words are a “current flows.” 

If the thumb be thrust into one end of a hose that is 
filled with water and held as shown, water will issue from 
the other end at the same instant. 


DYNAMIC ELECTRICITY. 


113 


But the water that issues is not the water pressed upon. 



KINDS OF BATTERIES. Batteries have been multi¬ 
plied until their names are legion. 

Those in common use are: 

The Gravity, Leclanche, Law, Diamond, Dry (Gass- 
ner’s), and the Bichromate. 

(The Dry Battery is a misnomer. There is no battery 
without water.) 

The Bichromate Battery is the best adapted to exper¬ 
imental use and can be made by any one. 

The Leclanche, Diamond, Law, and Gassner’s are for 
open circuits, such as ringing call bells. 

The Gravity is the one in universal use for telegraphy. 
It is used for closed circuits. 

The only one pictured and described is the one the 
pupil is directed to make and use. 

PRINCIPLES OF A BATTERY. 1. There must be two 
solids and one liquid. 

2. One solid must act upon the liquid more than the 
other. 

3. The greater the difference of chemical action, the 
stronger the battery. 









114 


DYNAMIC ELECTRICITY. 


bunsen’s cell or bichromate of potash battery. 

ITS CONSTRUCTION. 1. Choice of solids. 

2. Amalgamation of zincs. 

3. Preparation of carbons. 

4. Choice of liquid. 

CHOICE OF SOLIDS. In most batteries, zinc is one of 
the solids for three reasons: 

1. It acts readily on all acids. 

2. Its salts are very soluble. 

3. It is cheap. 

Before using the zinc plates, it will be best to amalga¬ 
mate them— 

1. To prevent local circuits because of impurities in 
the zinc. 

2. To prevent waste. 

3. To increase their conductivity. 

The zincs are easily amalgamated by taking two nap¬ 
pies and into one of them pouring a pint of water and a 
tablespoonful of sulphuric acid. 

Hold the plate upright. 



Fig 102. 






DYNAMIC ELECTRICITY. 


115 


Pour the dilute acid on the plate turning it and 
changing its ends. 

Change nappies and repeat. 

All this is done to clean the plates. 

Pour into the acid a teaspoonful of mercury and repeat 
all the former acts. 

By adding four per cent, of mercury to molten zinc 
before casting into plates, no amalgamation is necessary. 

The other solid is usually carbon for the following 
reasons: 

1. It does not act on the acid. 

2. It is a fair conductor. 

3. It presents a large internal surface because of its 
porosity. 

The carbon plate, so called, is really graphite and 
gas-carbon. 

Carbon is too poor a conductor and too brittle to be 
used alone. 

It is powdered and mixed with graphite, which is a 
good conductor, then made plastic with molasses, molded 
into plates about \ in. thick and of various sizes, and 
baked. 

CUTTING THE PLATES. To cut a zinc plate, make a 
deep scratch by repeated strokes with the end of a file and 
pour a little mercury into the groove. 

In about a minute, the plate becomes brittle along 
this line and may be safely broken. 

To cut a carbon plate, lay a straight edge on the plate 
and make a groove with a scratch awl. 

Turn the plate and make another over the first. 

The plate will break easily along this line. 

CHOICE OF LIQUID. There has been much experi¬ 
mentation to find a liquid that would do the following: 


116 


DYNAMIC ELECTRICITY. 


1. Excite the zinc after the action has begun. 

2. Increase the conductivity of the water. 

3. Absorb the hydrogen. 

It has been found on trial that adding bichromate of 
potash to dilute sulphuric acid, secures all these results. 

The acid decomposes the bichromate, liberating oxy¬ 
gen, which unites with the escaping hydrogen to form 
water, thus preventing polarization of the carbon plate 
by the accumulation of the hydrogen upon it. 

The action of the zinc upon the sulphuric acid forms 
sulphate of zinc, thus: 

Zn 2 +2H 2 S0 4 =2ZnS0 4 +2H 2 

This coating of sulphate of zinc would soon polarize 
the zinc plate, but as all the salts of zinc are soluble, this 
salt is at once dissolved by the liquid and the plate cleaned 
for further action. 

FORMULA FOR THE LIQUID. To one gallon of water 
add one and one-half pints of sulphuric acid and four 
ounces of bichromate of potash. 

Mix in an earthen vessel—never in a glass one. 

Stir well with a glass rod. 

Set aside to cool. 

SETTING UP THE BATTERY. For the pupil’s use 
take two one-quart Mason’s fruit jars and fill them two- 
thirds full of the battery solution. 

Cut the plates 1^ by 9 inches. Cut a piece of glass 
the same size to separate the plates. 

Have two similar jars nearly full of water and into 
these set the plates. 

Fasten connectors to the Zn and C for the attachment 
of wires. 

This applies to each element. 


DYNAMIC ELECTRICITY. 


117 



When it is desired to use the battery, lift the plates as 
shown, from the water to the battery jars and perform the 
experiment. 

Immediately return them to the water jars for cleans¬ 
ing. 

For convenience and heavier work, a battery may be 
set up as shown in 













118 


DYNAMIC ELECTRICITY. 



Fig. 104. 


For experimental purposes, the bichromate of potash 
battery is the most efficient of any in use. 

If set up as shown in Fig. 104, it may be immediately 
cleaned after using without the usual “mess” attendant 
upon the cleaning of batteries generally. 

By having the jars on a sliding base the plates may be 
arranged for vertical motion only and the battery jars 
pushed back and replaced by the water jars. 

On lowering the plates they are washed at once. 

CARE OF BATTERY. In the care of the battery de¬ 
scribed the most important thing to do after use is: 

1. To remove the plates from the solution. 






























ELECTRIC MEASUREMENTS. 


119 


2. To wash them at once. 

3. To keep the zincs amalgamated. 

TERMS USED. In the use of any battery, there are 
certain terms that may be new to the pupil. 

Among these are: Cell, Electrode, Excitant, Poles, 
Conductors, Non-conductors, Insulators, Amalgamation, 
Polarization. 

All of these have been explained. 

There are other terms that will now be named that 
come under 


CHAPTER XXVIII. 

ELECTRIC MEASUREMENTS. 

They are: Electromotive Force, Volt; Strength of 
Current, Ampere; Resistance, Ohm. 

ELECTROMOTIVE FORCE. Electromotive Force or E. 
M. F. is the difference of electric potential. 

It depends, in the battery, upon the kind of plates but 
not on their size. 

The E. M. F. of the battery can be increased by join¬ 
ing the cells in series, Fig. 103, or decreased by joining 
them in multiple arc, i. e., uniting all the zincs for one 
pole and all the carbons for the other. Why?- 

THE VOLT. E. M. F. is measured in volts. 

A volt is the unit of E. M. F. and is represented prac¬ 
tically by the E. M. F. of the Daniell Cell. 

STRENGTH OF CURRENT. The strength of the current 
is the quantity of electricity that flows across any section of 
the circuit in one second of time. 

With a given resistance, it varies as the E. M. F. 


120 


ELECTRIC MEASUREMENTS. 


THE AMPERE. The ampere is the current strength 
represented by an E. M. F. of one volt divided by a re- 
sistance of one ohm. 

RESISTANCE. Resistance is that which opposes the 
flow of an electric current. 

It is measured in ohms. 

THE OHM. The ohm is the unit of resistance and is 
the resistance of a column of mercury .112— inches in 
diameter and 41.73 inches in length. 

In practice, the ohm is the resistance of 250 ft. of No. 
16, or 10 ft. of No. 30, copper wire. 

ESTABLISHMENT OF UNITS. At a meeting of the 
International Electric Congress in Paris, in 1884, a system 
of Electric Units was established and is accepted as au¬ 
thoritative. 

Those in most common use are: The Volt, The Ohm, 
The Ampere, The Watt. 

The basis of the entire system is the Erg, which is a 
mechanical unit and represents the work done by the 
movement of 1 gramme 1 centimeter in 1 second. 

Its symbol is C. G. S. These letters are the initials 
of centimeter, gramme, and second, which are the three 
factors of the Erg. 

The following are some of the terms used, with their 
abbreviations. 

E. or E. M. F. = Electromotive Force. 

C = Current Strength. 

P- D. = Potential Difference. 

V = Volt. 

amp. = Ampere. 

R = Resistance. 

I = Intensity. 

R ' — Internal Resistance. 


ELECTRIC MEASUREMENTS. 


121 


r = External Resistance. 

L = Length of Wire. 

A = Area of Cross Section. 
Om. — Ohm. 

W. = Watt. 

H.P. = Horse Power. 


EQUIVALENTS AND FORMULA. 1 Erg = The Unit 
of Work. 

10 7 Ergs = 1 W. 

746 W = 1 H.P. 

1 W — 1 Vxl amp. or 1 Volt-ampere. 


E = CR or C(R'+r) 


»ri 


R = 


or 


E 

IP+r 


State the laws for each of the above formulae. 

It may be well for the pupil to know the names and 
uses of the following: 

Voltmeter, Ammeter, Potential Indicator, Ohmmeter, 
Rheostat, Lightning Arrester, Wattmeter. 



122 


EFFECTS OF ELECTRICITY. 


CHAPTER XXIX. 

EFFECTS OF ELECTRICITY. 

The effects of electricity may be classed under the 
following heads: 

1. Electromiagnetic. 

2. Electro-thermal. 

3. Electro-chemical. 

ELECTRO-MAGNETIC EFFECTS. On close inspection, 
it will be found that all the practical applications of elec¬ 
tricity are wholly dependent upon its magnetic effects. 

By this is meant, that, with possibly a single exception, 
the dynamo and the electromagnet are capable of perform¬ 
ing any experiment in electricity. 

Batteries are now used because they are convenient 
and cheap. 

The applications of the electromagnet are: 

1. Call Bells. 

2. Fire Alarm. 

3. Telephone. 

4. Telegraph. 

5. Induction Coil. 

6. Dynamo. 

7. Motor. 

ELECTROMAGNET. The electromagnet is a bar of iron 
or steel magnetized by lines of force from an electric current. 

If the bar is soft iron it becomes a temporary magnet. 

If of steel, a permanent one. 

The following experiment shows that lines of force 
surround a wire carrying a current and also leads us to see 


EFFECTS OF ELECTRICITY. 


123 


how a bar of iron or steel may become magnetic from the 
presence of a current. 

Pass a copper wire through a card and join the ends 
to the poles of a battery. 

Sprinkle fine iron filings around the wire. 

Gently tap the card. 



Fig 105. 


Make a few coils of insulated copper wire around a 
steel bar and, with the current on, slide the bar through 
the coil from one end to the other several times, each 
time the same way. 

Plunge one end of the bar into iron filings. 









124 


EFFECTS OF ELECTRICITY. 



Turn off the current and most of the filings remain. 
The magnet is a permanent one. 

Bend a bar of soft iron 1 in. in diameter and 10 in. 
long in the form of a horseshoe. 

Make the ends closely fit a plane surface. 

Wind an insulated copper wire (Bell wire No. 16) 
around the bar, as shown in 



Fig. 107 . 


Close the circuit and apply to the iron filings as before. 
The filings cling to the bar. 

Turn off the current and the filings fall. 

The magnet is a temporary one. 


























EFFECTS OF ELECTRICITY. 


125 


The relative positions of the surface molecules of the 
bars were changed. 

Those of the steel maintained the new relations, while 
those of the iron returned to the former ones. 

In proof of this, take a very sharp razor and apply the 
magnet just made to the back of the razor, using a strong 
current. 



Fig. 108. 

The razor will not shave as before. (Tyndall’s experi¬ 
ment. ) 

The molecules are now faced about toward the ends of 
the blade and must be reset before using. 























126 


EFFECTS OF ELECTRICITY. 


The razor is a permanent magnet. 

Now use the electromagnet to lift pocket knives, 
needles, tacks, and other iron and steel objects. 

Put an iron filing under your finger nail and withdraw 
it with the magnet. 

What does this teach? 

In any experiment in which the electromagnet is used 
to lift objects, will it instantly let go of them upon shut¬ 
ting off the current? 

If not, it has residual magnetism. 

To remove this property from common iron, treat as 
follows: 

Place the iron rods or wires to be used for cores in a 
short steam pipe and put a screw cap on each end. 

Keep this pipe red hot for six hours and cool slowly in 
ashes. 

On removal of the iron, it will be found soft and 
nearly pure. 

It has been decarbonized. 

It will now act instantly if used as a core for a magnet. 

If the pupil wishes a strong electromagnet he should 
make it short and stumpy, with the distance between 
the arms three times the thickness of one of them. 

The wire wound on should not make the thickness^ 
the coil more than three times the diameter of the core. 

CALL BELLS. Annunciators in hotels and call bells in 
most dwellings exist because of the electromagnet. 

A one or two-celled battery of the Leclanche type is 
screened from view and wires lead from this battery to 
the push-button and the bell. Some bells are rung by a 
miniature dynamo. 


EFFECTS OF ELECTKICIT Y. 


127 



THE FIRE ALARM. The fire alarm is a signal given 
by a bell struck by the action of an electromagnet. 

The two points of difference between it and the call 
bell are: 

1. The push button is locked up and the key left near 
the Fire Alarm Box. 

2. The bell at the engine house is a very large one and 
acted upon by a large magnet. 

When the signal is given an annunciator in the engine 
house discloses the number of the Box. 

All the connections are essentially the same as in Fig. 
109. 

SELF-ACTING FIRE ALARM. Signals may be given 
and the fire company appear upon the premises while the 
occupants of the building are unconscious of danger. 

The self-acting fire alarm gives the signal by means of 
a thermostat. 









































128 


EFFECTS OF ELECTRICITY. 


A THERMOSTAT. A thermostat is an instrument for 
regulating temperature by the unequal expansion of metals. 

It consists of an elongated glass bulb partly filled with 
mercury and having two short platinum wires enclosed in 
its ends. 

These thermostats are placed on the ceiling of the 
room several feet apart, with wires joining the platinum 
electrodes to a battery. 

When a fire breaks out in such a room, the heat being 
greatest at the ceiling, the mercury of the thermostat 
expands and completes the circuit and the signal is given. 

A thermostat is usually set to complete the circuit at 
110° F. 

The pupil can easily make one. 



Blow the glass bulb and melt the glass around a No. 
30 platinum wire in one end as shown. 

Pour mercury into the bulb until about two-thirds full. 

Hold this bulb in water at 110 F. with the open end 
above the surface of the water. 

Mark the surface of the mercury upon the neck of the 
bulb, after giving time for expansion. 

Place a platinum wire in the open end of the bulb 
down to the mark and melt the glass around it. 

To use this thermostat properly, connect to the battery 
and bell, Fig. 109, and warm gently with an alcohol lamp. 

These thermostats are usually concealed by the last 
thin coat of plastering. 






THE TELEPHONE-THE TELEGRAPH. 


129 


CHAPTER XXX. 

THE TELEPHONE—THE TELEGRAPH. 

THE TELEPHONE. The telephone is an instrument for 
impressing sound waves upon an induced electric current. 

This is the transmitting instrument. 

THE MICROPHONE. A microphone is an instrument 
by which minute sound waves impressed upon an induced 
electric current are made audible. 

This is the receiving instrument. 

CONDITIONS OF TELEPHONY. The conditions of te¬ 
lephony are: 

1. An Electromagnet. 

2. A Vibrating Disk. 

3. A Yielding Insulator (at present, carbon). 

4. A Conducting Wire. 

5. A Battery. 

A call bell is a necessary accompaniment of the tele¬ 
phone for exchanging signals. 

The telephonic outfit is easy of construction for demon¬ 
stration of the principles involved. 

See “Physics by Experiment.” (Shaw.) 






















130 


THE TELEPHONE-THE TELEGRAPH. 


The telephonic current may be represented by a line 
of varying width. 

The intervals represented indicate the effect of sound 
waves upon the passing current. 


Fig. 112. 

Evidently the instruments are duplicated at each sta¬ 
tion. 

The telephonic circuit may be represented as in 



Fig. 113. 


THE TELEGRAPH. The telegraph is a mode of com¬ 
munication by signals made by interrupting an electric 
current. 

The conditions of telegraphy are : 

1. A Transmitter or Key. 

2. A Receiver or Sounder. 

3. A Connecting Wire. 

4. A Battery. 

To the above is added the relay for long distance 
telegraphy. 

The relay is a local battery to strengthen the effect of 
the sounder. 

By making the circuit continuous on two different 
routes a relay may become a repeater. 











THE TELEPHONE-THE TELEGRAPH. 


131 


In the English system of telegraphy, the message is 
read by the eye from the deflections of the needle of a 
galvanometer. 

In America, the message is read by the ear from the 
clicking of the sounder.. 

The following figure represents the interrupted tele¬ 
graphic current. 


Fig. 114. 

Read the above message. 

The Morse alphabet is as follows: 


a- 

J- 

s 

1- 

b- 

k- 

t — 

2 - - 

c- 

1 

ll- 

3- 

d- 

m- 

v- 

4 .... 

e - 

n- 

w-- 

5- 

f- 

o - - 

X - 

6. 

g- 

P. 

y -- -- 

7- 

h ---- 

q-- 

z - - - - 

8- 

i -- 

r - -- 

& - --- 

9- 


0 


All operators must understand the same code of sig¬ 
nals. 

A great mystery in telegraphy is this: How can two 
messages be sent the same, or opposite ways, over the 
same wire at the same time. 

If the same way, the system is called the diplex, 

If sent the opposite way, the duplex. 









132 


THE TELEPHONE — THE TELEGRAPH. 


In the diplex system two keys are used at the sending 
station and two sounders at the receiving station. 

Two currents of unequal strength are used, giving the 
receiving operators, by their relays, signals of different 
intensity. 

In the duplex system, when messages are sent simul¬ 
taneously in opposite ways over the same wire, each 
operator controls the sounder of the other, but not his 
own. 

Since simultaneous means to us at the same instant, as 
judged by our senses, and since electric movements are 
too rapid for such judgment, the exchange of signals is 
effected by each operator transmitting and receiving at 
the same time, each taking advantage of the intervals 
given by the other. 

The following diagram from Gage’s Physics will 
lead the pupil to see how messages are sent and what part 
the earth plays in the circuit. 



INDUCTION COIL. An induction coil is an instrument to 
increase the electromotive force of a battery. 













electro-thermal effects. 


133 


For making, using, and experimenting with one, the 
pupil is referred to a small book on Induction Coils, 
How Made and How Used, published by D. VanNostrand 
& Co., N. Y. Price, 50 cents. Induction Coils. G. E. 
Bonney. Macmillan & Co., N. Y. Price, $1.50. 

The accompanying drawing from Poyser’s “Magnetism 
and Electricity” is given for its simplicity and for its 
value to a pupil in showing him how the parts of an 
Induction Coil are connected. 



CHAPTER XXXI. 

ELECTRO-THERMAL EFFECTS. 

Among the wonders of electricity are its heating 
effects. 

Electric Lights, Melting of Refractory Substances, 
and Welding, are modern phenomena. 

The principle involved is: 

That the arrest of motion produces heat. 








134 


ELECTRO-THERMAL EFFECTS. 


The more rapid the motion and the more sudden the 
arrest, the higher the heat. 

The rapid blows of a hammer upon a piece of cold iron 
may forge a horseshoe nail. 

Electricity moves 288,000 miles per second. 

If proper resistance be interposed to such velocity, the 
highest heat may result. 

Connect the poles of a strong battery to a piece of 
platinum wire No. 30, and by the current bring the same 
to a red heat. 

Bend the wire and dip it into a goblet of water. 



Fig. 117. 


The platinum wire is a poor conductor. 

The great resistance of the wire arrests the motion of 
the current and heat results. 

On dipping the middle of the wire into the water, its 
ends are brought to a white heat. Why? 

It is in the use of this principle that electric lighting 
has become practical. 

THE ARC LIGHT. In this form of light two carbon 
pencils are interposed between the poles of a current from 
a dynamo. 

Carbon offers high resistance to the current. 

The pencil at the positive pole becomes shorter and 




ELECTRO-THERMAL EFFECTS. 


135 


slightly concave, while that at the negative pole becomes 
convex and wastes less rapidly. 

The particles of carbon carried across the arc glow at 
a white heat, and immediately unite with the oxygen of 
the air to form C0 2 . 




Fig. 118. 


The distance between the carbons is controlled by a 
regulator operated by the current. 

This regulator is usually above the light and moves the 
upper pencil only. 

By a lever controlling the armature of an electro¬ 
magnet, a strong current separates the pencils and in¬ 
creases the resistance. 

A weak current causes them to approach and lessens 
the resistance. 


















136 


ELECTRO-THERMAL EFFECTS. 


The effect of the regulator is to keep the pencils at 
about the same distance apart, but producing, at best, an 
unsteady light. 

These lamps are pendant or placed on poles or masts. 

If pendant, the number of lamps is increased, each 
illumines a small area with great intensity. 

If the lights are elevated on poles or masts, the num¬ 
ber is lessened, the area illuminated is larger, and the 
intensity of the light is less. 

Increasing the number of lamps upon the masts lessens, 
but does not overcome, the difficulty. 

The mast system is being discarded except for beacon 
lights. 

Owing to the flickering of the lights, the imperfect 
composition of the carbons, and the daily cleaning of the 
lamps, they are plainly unfit for house use. Hence, 

THE INCANDESCENT LAMP. An incandescent light is 
one that glows but does not consume. 

After much experimenting, carbon filaments from the 
bamboo were found to offer high resistance to the current 
and to glow for days under its influence, providing they 
were in a perfect vacuum. 

To obtain such a vacuum required a great outlay of 
time and capital. 

By the use of the mercury pump, such a vacuum was 
obtained and the incandescent light became at once 
almost universal. 

A metallic pump called the Berrenberg pump is now 
used to produce the vacua in incandescent lamps because 
of its rapid action and the perfection of its exhaust. 

Both cylinder and plunger are metal. The vacua are 
free from the vapor of mercury and more nearly approach 


ELECTRO-THERMAL EFFECTS. 


137 


the absolute vacuum than can be obtained by the mercury 

pump. 

This pump exhausts 600 lamps in twenty minutes. 

The life of an incandescent lamp varies from 600 to 
800 hours. 

The incandescent light is clear, steady, attractive, and 
is the cheapest light known, not excepting kerosene. 



The heating effects of electricity are of great utility in 
firing exj^losives. 

AN EXPLODER. A small copper cap filled with the 
fulminate of mercury has two insulated copper wires 
leading from it to the battery or dynamo. 

This cap is placed in the powder or dynamite. 

The length of the wires insures safety when the cur¬ 
rent is applied. 

It is in this way that submarine blasting may be carried 





138 


ELECTRO-THERMAL EFFECTS. 


on or that a marine torpedo becomes more dangerous than 
the entire armament of a man-of-war. 



Fig. 120. 


ELECTRIC WELDING. Welding by electricity is a 
simpler process than in the forge. 

The usual way of welding is to “upset” the ends of 
the bars and lap them one upon the other. 

Upon heating, the lap is reduced to the size of either 
bar by pounding. 

Not so in electric welding. 

The ends of the bars are rounded and pressed together. 

A powerful quantity current is applied at the joint and 
the welding takes place in the center first. 

All oxidised particles or impurities are forced to the 
surface which is welded last. 

Bars one and one-fourth inches in diameter may be 
welded in forty seconds. 

The bars become red hot only about two and one-half 
inches from the joint, the time of w T elding being too short 
for the heat to be transmitted farther. 

This form of welding may be used when the heat of 
the forge can not be applied, and where the lap method is 
impossible. 

Tubes, pipes, cables and wholly different metals can 
be welded by this process. 

The "welding of different metals is possible only when 
they can be given different degrees of heat. 

The machine in use for this purpose is called a welder, 
the current in which is controlled by a treadle. 





electro-chemical effects. 


139 

One bar is held rigid, while the operator forces the 
other against it by a lever. 

What may be the outcome of this unexpected applica¬ 
tion of electricity to welding, soldering, and riveting, no 
one can predict. 


CHAPTER XXXII. 

ELECTRO-CHEMICAL EFFECTS. 

The electro-chemical effects of electricity are such as 
overcome or establish chemical affinity. 

They may be classed as : 

1. Electrolysis. 

2. Synthesis. 

3. Electrotyping. 

4. Electroplating. 

5. Reduction of metals from solutions of their ores. 

6. Storage Batteries. 



Ftg. 121. 














140 


ELECTRO-CHEMICAL EFFECTS. 


ELECTROLYSIS Electrolysis is the decomposition of an 
electrolyte. 

An electrolyte is the liquid to be decomposed. 

An electrolysis cup is a vessel in which decomposition 
by electrolysis takes place. 

The electrodes are platinum terminals in the electro¬ 
lysis cup. 

The elements appearing at the positive electrode are 
negative and are called anions, those drawn to the negative 
electrode are positive and are called cathions. 

OPERATION. Fill the electrolysis cup three-fourths 
full of water in which are a few drops of H 2 S0 4 to in¬ 
crease its conductivity. 

Fill the tubes with water and invert, without admit¬ 
ting air, over the electrodes. 

Apply a current from a two-celled bichromate battery 
and watch the result. 

Label the electrodes and the tubes. 

Test the gases. 

The process by which H is liberated at the negative 
electrode and O at the positive has never been seen. 



Fig. 122. 










ELECTRO-CHEMICAL EFFECTS. 


141 


It is believed that the molecules of the water, like 
those of the magnet, lie in different directions as shown 
in Row 1 in Fig. 122. 

On applying the current, the molecules are under stress 
and are polarized and appear as in Row 2. 

From the continued effects of the current they ex¬ 
change atoms, the O of the molecule next to the positive 
electrode becomes free and the water presses it upward. 

Its H seizes the O of the next molecule, forming a new 
molecule of water. 

Thus a series of decompositions and recompositions 
take place until the negative electrode is reached. 

Here the H is set free and is pressed upward by the 
water 

Examine Row 3. 

The shaded parts represent H and the lighter parts O, 
in each oval figure. 

This process is not known to be true, since by means 
of no device has the process here described been seen. 

All other substances electrolyzed act in the same way, 
the metals appearing at the negative electrode and the 
non-metal at the positive. 

This explanation is purely theoretical. It accords 
with the facts and is the one generally accepted. 

If the poles are changed the gases change also. 

PRINCIPLE. In electrolysis the metals are deposited on 
the negative electrode. 

The above principle is the one guiding all the work in 
electrolysis, electrotyping, electroplating and in the stor¬ 
age battery. 

Try a weak solution of table salt, sugar of lead, sul¬ 
phate of copper, nitrate of silver. 


142 


ELECTRO-CHEMICAL EFFECTS. 


An electrolysis cup in the form of a cell may be easily 
made. 



Fig. 123. 


Use pieces of plate glass 3x4 inches and place a solid 
rubber cord between them as shown in Fig. 123. 

Place No. 24 platinum wires on the cord about one- 
half inch apart. 

Press the plates together and put on each end a band 
of tin one-fourth of an inch wide. 

The wires will be pressed into the rubber. The pro¬ 
jecting parts should be insulated from each other and 
brought outside the cord to the end of the cell. 

Here they should be joined to the binding posts. 

The wires may now be covered with marine glue or 
paraffin. 

This cell may be used for all common acids, alkalies, 
and their compounds. 

The best use of the cell is to show, by projection, 
electrolytic action on the screen. 

SYNTHESIS.—Synthesis, in electro-chemistry, is the 
formation of compounds by the action of an electric current. 

If the tubes over the electrodes for collecting II and 
0 be united into one tube and wires inserted near the 













ELECTRO-CHEMICAL EFFECTS. 


143 


top, the escaping gases mix and may be exploded by the 
electric spark. 



The tube now becomes a eudiometer. 

The mixed gases should not occupy more than one- 
fifth of the space within the tube. 

The heat of the electric spark restores the chemical 
affinity and water is formed. 

Since chemical affinity in the battery developed a force 
that overcame chemical affinity in the molecules of the 
water, and since the force of the electric spark restored 
the chemical affinity between the gases O and H, it is 
proper to ask the question, Are chemical affinity and 
electricity identical? 


















144 


ELECTRO-CIIEMICAL EFFECTS. 


Certain it is that chemical affinity always develops 
electricity and electricity may bring about chemical 
action. 

They may be different names for the same force. 

ELECTROTYPING.—Electrotyping is the process of mak¬ 
ing a metallic deposit by the electric current, upon a mold 
taken from type. 

A wax impression of the type is taken and coated 
with plumbago. 

This impression is now placed in a bath of sulphate 
of copper and joined to the negative pole of a battery or 
dynamo. 

The positive pole is joined to a copper plate to keep 
the solution strong. 

When the current is applied, a deposit of copper is 
made upon the plumbago. 

The thickness of the deposit is about one-sixteenth of 
an inch. 

The wax is then melted off and a backing of molten 
type-metal poured on. 

These plates will give fine impressions for thousands 
of copies. 

All of our standard books are printed from such 
plates. 

The process of preparing these plates requires from 
four to twelve hours. 

STEREOTYPE PLATES.—Stereotype plates, though 
not prepared by the electric current, may be described 
here because of their daily preparation and use. 

Such plates do not give as good print or last as long 
as electroplates. 

Our daily papers and cheap books are printed from 
stereotype plates. 


ELECTROPLATING. 


145 


Stereotype plates are prepared from type of special 
form. 

Plaster of Paris or papier-mache is impressed upon 
the type. 

When removed and dried, the cast is filled with 
molten type-metal which, after cooling, is removed from 
the plate. 

The plate is planed to uniform thickness before using. 


CHAPTER XXXIII. 

ELECTROPLATING. 

Electroplating is usually the process of depositing the 
more valuable metals upon baser ones, either for protection or 
ornament, or for both purposes. 

The metals to be deposited are placed in solution 
forming a bath which is kept strong by the presence of 
the same metal in some form attached to the positive pole 
of the battery. 

The articles to be plated must be perfectly clean, 
washed in acid, alkali, and water, and in no case touched 
by the hand. 

On their removal from the bath, they have a dull 
rough appearance which is removed by burnishing. 

Nickel has replaced silver for common articles be¬ 
cause it is cheaper, harder and wears longer. 

Almost anything can be plated by coating it first with 
some mineral or metallic substance that will take the 
deposit. 

REDUCTION OF ORES. Since the introduction of 
the dynamo for lighting and motor power it has come to 


146 


ELECTROPLATING. 


play an important part in the reduction of ores and refin¬ 
ing of metals. 

The ores are roasted or pulverized and dissolved by 
the use of solvents and the metal deposited by elec¬ 
trolysis. 

Aluminium exists in abundance in the common clays, 
but is difficult of extraction. 

Aluminium compounds are fused in a carbon crucible. 

Bauxite, a preparation of alumina or clay, is added. 

A strong quantity current is applied to this fused 
bath and aluminium is drawn off and alumina supplied. 

This metal has long been a chemical curiosity, but it 
is now a useful and ornamental article of commerce, due 
to the improved methods of extraction. 

Aluminium is a ductile, malleable, bluish white metal, 
as light as glass, its specific gravity being 2.56. 

Owing to its lightness and ready transmission of heat, 
it is thought that this metal will be much used in cul- 
inary arts. 

STORAGE BATTERIES. Storage batteries are batter¬ 
ies which receive active electric energy and store it as 
cheminal energy. 

Electricity cannot be stored. Its energy can. 

Flowing water may turn a wheel that lifts a weight. 

This weight has potential energy and may in turn do 
the work given it less the loss by friction. 

But the water is not stored. 

Storage batteries work upon the following principle: 
Chemical potential is produced upon plates dissimilarly pre¬ 
pared by the electric current. 

Chemical energy is stored up in the friction match. 

The phosphorus covers the sulphur which in turn 
covers the sugar that coats the wood. 


ELECTROPLATING. 


147 


A little friction fires the substances in the order 
named. 

The chemical energy thus freed as heat about 
600° F. 

In like manner, electric energy is stored in the Faure 
battery. 

Plates of sheet lead one-eighth of an inch thick are 
coated with a paste made of red lead and sulphuric acid 
on which is placed an insulation of felt. 

These plates are rolled together and placed in a jar 
of water acidulated with sulphuric acid. 

By electrolysis, the red lead is decomposed and sul¬ 
phate of lead is formed on both plates. 

Water is also decomposed and the escaping O forms 
dioxide of lead on one plate and the escaping II forms 
monoxide of lead, or as it is called, spongy lead, on the 
other. 

On using the battery, the chemical reaction restores the 
sulphate of lead and the battery action ceases. 

The charging of the battery consists in applying the 
electric current to the plates to change the sulphate to 
dioxide and spongy lead as before. 

Improvements have been made in this process, but 
the high expectations concerning storage batteries have 
met disappointment. 

Such batteries work with declining energy. 

If continued force is required, the batteries must be 
duplicated so that while some are in use, the others may 
be charged. 

They are objectionable on account of their great 
weight, a common cell weighing 130 lbs. 

The duration of the cell depends upon its make, size 
and the work to be done. 


148 


THE DYNAMO. 


CHAPTER XXXIV. 

THE DYNAMO. 

DEFINITION. A dynamo is a machine which changes 
mechanical energy to an electric current. 

It is a modern invention, and, in its operation, is 
based on former discoveries embodied in the following 

PRINCIPLES. 

1 Magnetism and electricity may each be changed to 
the other by inductive action. 

2. Mechanical energy may be changed to an electric 
current by such movement as causes the plane of a 
circuit conductor to cut a varying number of magnetic 
lines of force. 

3. The direction of the current is at right angles to 
the direction of the inducing lines of force. 

The intimate relation between electricity and magnet¬ 
ism was discovered by Jean Oersted, a Dane, in 1820. 

In the same year, Arago and Davy, independently, 
discovered that electricity may be changed to magnetism, 
but to Michael Faraday is due the credit for discovering 
that magnetism may be changed to electricity. 

He also discovered that mechanical movement of a 
circuit conductor in a magnetic field produces an electric 
current, thus proving that mechanical energy may be con¬ 
verted into current electricity. 

The immediate result of this discovery was the first 
dynamo, October, 1831. 


THE DYNAMO. 


149 



In the machine represented above the disk is copper. 

The wires connect the axis and the edge of the disk 
to a galvanometer. 

See also p. 17 in Electricity In Daily Life, 

In the operation of the dynamo of the present, the 
conditions for effecting this change are. 

1. A source of mechanical energy supplied, usually, 
by a steam engine. 

2. The presence of powerful magnets. 

3. A circuit conductor. 

4. The rotation of one of either the magnets or con¬ 
ductor in the immediate presence of the other. 












150 


THE DYNAMO. 


The manner of action as required by Principles 2 and 
3 is illustrated in 



Fig. 126. 


From- the above drawing it appears that the plane of 
the rotating coil cuts more lines of force when in position 
A than when in position B. 

It occupies, therefore, in each rotation positions of 
maximum and minimum magnetic potential. 

The effect jiroduced at each of such change of posi¬ 
tion, is a transitory current in the coil. 

It will be observed also, that the direction of the cur¬ 
rent changes with the change of direction of the coil 
according to Principle 3, which is also stated in Lenz’s 
Law, viz: the direction of currents induced by motion of a 
conductor or magnet is always such as to produce forces 
opposing the motion which generates them. 

If these alternating currents are not changed in direc¬ 
tion, the machine is called an alternating current dynamo. 

Such currents may, however, be changed to a current 
of one direction by means of a commutator. The 
machine is then called a direct current dynamo. 

It will be seen from this that there is from no dynamo a 
continuous current such as that from a battery. 
















































THE DYNAMO. 


151 


The current is made as nearly continuous as need be 
by commutation and rapid succession of the transitory 
currents. 

In the direct current dynamo, the result may be a cur¬ 
rent similar to the telephonic current, except that the 
waves occur at regular intervals. 

From Principle 2 it appears that the current is gen¬ 
erated by a variation in the number of lines of force cut 
by the plane of a circuit conductor in a given time. 

From this it follows that the greater the number of 
such lines cut in a given time the greater the current 
strength. This may be further increased by an increase 
of the strength of such lines of force. 

An increase in current strength effects an increase in 
E. M. F., the resistance remaining the same. 

Since resistance in a conductor varies inversely as 
the area of its cross section, it is evident that the 
E. M. F. of the dynamo current may be varied by a 
variation in the number and size of the wires used. 

Hence the strength of the dynamo current depends, 
primarily, upon the size and strength of its magnets. 

It may also be varied by means of a transformer. 

A Transformer is an instrument by which the E. M. F. 
of a current is diminished. 

It is essentially an inverted induction coil, without 
the current-breaking apparatus. 

It is evident therefore that it can be used only with 
an alternating current dynamo. 

In use, its high resistance coil is connected with the 
dynamo and its low resistance coil with the lamp, or 
other circuit. 

What is true of one coil is true of each of any num¬ 
ber of coils that may be rotated. 


152 


THE DYNAMO. 


Each coil adds its quota to the current at each passage 
from a position of maximum to one of minimum mag¬ 
netic potential, and vice versa. 

Hence it will be seen that quantity of current, or Am¬ 
perage, depends primarily, upon the number of coils used, 
the number of maximum and minimum points of magnetic 
potential in each rotation, and speed of rotation. 

Dynamos may therefore, by different arrangement of 
parts, be made to afford a current of high E. M. F. or 
Voltage, and small quantity of low Amperage, or on the 
other hand a current of high Amperage and low Voltage. 

In electric lighting by use of the arc lamp, a dynamo 
affording a current of the former kind is used owing to 
great resistance of the lamps, while in incandescent 
lighting a dynamo affording a current of the latter kind 
is needed. 

The essential parts of a dynamo are the field magnets, 
the armature, the commutator, and the brushes. 



The field magnets are electro magnets except in small 
machines. 

























THE DYNAMO. 


158 


T^he armature consists of an iron ring, or cylinder, or 
framework of iron, upon which are wound the coils of 
insulated wire, the whole mounted upon a shaft for rota¬ 
tion. 

The ring or cylinder of iron is called the core, and 
consists of layers of soft iron insulated from each other 
and from the shaft. 

The core serves to lead the lines of force nearer the 
center of the armature and hence more certainly through 
the coils, since it offers less resistance than the air. 

It also by reaction upon the surrounding field mag¬ 
nets increases the intensity of the magnetic field. 

In a direct current dynamo each coil is connected to a 
bar of copper fastened upon the shaft and insulated from 
it and from each other. 

These bars together form the commutator. 

The coils may be connected to each other and to the 
segments of the commutator thus forming a closed circuit 
armature. 

When the coils are independent of each other but are 
connected to the segments of the commutator they form 
an open circuit armature. 

In an alternating current dynamo, the commutator is 
displaced by two flat metal rings mounted upon the 
shaft and insulated from it, to which the coils are con¬ 
nected and which serve as a means for collecting the cur¬ 
rents. 

In all machines, the currents are collected by means 
of thin layers of copper or layers of copper wdres 
soldered together at one end and held in contact with the 
commutator or collecting ring at the other. 

These are the brushes:— 


154 


THE DYNAMO. 




In the work of the steam engine, a variation in the 
energy needed to overcome a necessary variation in re¬ 
sistance is effected by means of a governor. 

In the work of the dynamo, where steadiness is 
required the same end is reached by means of a shunt. 

A shunt is a loop in an electric conductor. 



It is evident from the above drawing that the current 
will divide at the point A, and that the current travel’s- 





THE DYNAMO. 


155 


ing the two parts of the loop will be inversely as the 
resistance of each. 

The resistance in the shunt may be varied at will by 
means of resistance coils. 

This shunt may have in it the field magnets of a 
dynamo. 

It is evident from the above drawing that if there is 
introduced into the main circuit an increased resistance, 
such as the turning on of more lamps, the starting of 
electric cars or the passage of the same up hill there will 
be deflected to the shunt an increased current. 

This increased current, traversing the coils of the 
field magnets, will, according to Principle 1, increase 
the magnetism of these magnets which will in turn, 
according to the same Principle, increase the electric 
energy to overcome the increased resistance. 

Decreasing the resistance of the main circuit reverses 
these processes. 



Fig. 131. 






























156 


THE DYNAMO. 


A dynamo whose winding includes a.shunt is called a 
shunt wound or constant potential dynamo. 

If the current traverses a single circuit, passing in 
series the armature, brushes, field magnets, and the exter¬ 
nal circuit, the dynamo is called a series wound or con¬ 
stant current dynamo. It is evident that its current 
varies directly as the resistance of the external circuit. 



If the main circuit and shunt both traverse the field 
magnets, the dynamo is compound w r ound. 

It is a constant potential dynamo. 

The shunt may also include a small machine whose 
field magnets are permanent steel magnets, the current 
from which is used to excite the field magnets of the 
large machine. 

































THE DYNAMO. 


157 



Fig. 133. 


Separate excitation is accomplished also exclusively by 
means of a small electro-magnet machine, no part of the 
current of which passes through the armature of the large 
machine. 

It is seen from what has been said concerning the action of 
the dynamo that next to mechanical energy, magnetism is an 
absolute prerequisite for the generation of an electric current. 

Since in large machines the magnets used are electro¬ 
magnets, it may be asked, whence the magnetism with 
which mechanical energy begins the transformation? 

It is found that the field magnets in process of manu¬ 
facture, being constantly under the magnetic influence of 
the earth, become permanently magnetic to a slight 
degree. 

This magnetism is called residual magnetism and 
sei’ves to begin the action of the dynamo. 





























158 


THE ELECTRIC MOTOR. 


CHAPTER XXXV. 

THE ELECTRIC MOTOR. 

DEFINITION. An electric motor is a machine which 
changes an electric current to mechanical energy. 

ITS PRINCIPLE. 

Its principle is the converse of Lenz’s Law, previously 
stated. 

The mechanical energy applied in rotating the arma¬ 
ture of a dynamo induces magnetism and electricity and 
consequent attraction, both magnetic and electric, which 
is a reaction in opposition to the mechanical movement. 

It is clear then that if the mechanical energy is not 
sufficient to overcome this reaction the armature will cease 
to rotate, and that, minus loss by friction, the mechanical 
energy applied is a measure of the electric energy 
developed. 

If two dynamos be connected, and mechanical energy 
applied to one it passes as electric energy to the other, 
producing the same conditions of potential difference and 
consequent reaction. 

Since in the second machine nothing save friction 
opposes this reaction its armature rotates, but in a direc¬ 
tion opposite to that of the first. 

The mechanical energy required at the armature of the 
first is thus reproduced, less the friction of the two 
machines, by the armature of the second. 

Since the friction of a motor or dynamo is only that of the 


THE ELECTRIC MOTOR. 


159 


shaft of its armature, it is clear that these machines reproduce 
more of the energy given them than any other known machines, 
and is often more than 90 per cent, of it. 

The dynamo made possible the motor, the motor makes 
possible the economical application of mechanical energy 
at points far distant from the point of its generation. 

What may be accomplished in the future by use of 
these machines it is impossible to know. 

THE ELECTRIC STREET CAR. 

Beside the usual car and track the necessary condi¬ 
tions for street car propulsion by means of electricity are: 

1. One or more dynamos. 

2 . A conductor, usually over the center of the track 
leading the current to the car. 

3. A conductor, usually under the center of the track 
to which each of the rails is connected, leading the current 
from the car to the dynamo. 

4 . An electric motor to propel the car. 

The conductors leading to and from the car are care¬ 
fully insulated to prevent loss of electricity and accident. 

The manner of operation is indicated in Fig. 134. 

It is evident that the car completes the circuit between the 
conductors at whatever point it may be. 

The armature in most of such motors makes about 
seven to ten revolutions to one revolution of the car 
wheel. 

This change in rate of motion is effected by means of 
gearing, the change illustrating the general law of 
machines, that velocity may be exchanged for intensity, 
no loss occurring save by friction. 

In the gearless motor, however, the armature makes 
the same number of revolutions, and the axle may serve 
as the shaft of the armature. 


160 


THE ELECTRIC MOTOR. 



With it, greater dynamo strength is required, however. 

The motor armature has as usual in the dynamo two 
brushes, one leading the current in and the other leading 
it out. 

The motorman in controlling the movement of the car 
changes its direction by changing the entering current 
from one of the brushes to the other, as it passes through 
the motor. 



























THE ELECTRIC MOTOR. 


161 


This change is effected by means of a switch con¬ 
trolled by a lever. 

In going up grade or in starting the car the amount 
of energy is controlled by means of a rheostat which is 
operated by a lever. 

A rheostat is an instrument by means of which a resist¬ 
ance, varied at will, is opposed to the passage of an electric 
current. 

To stop the car, the motonnan breaks the circuit be¬ 
tween the conductors at the rheostat, and uses the brake. 

The switch and rheostat are placed under the car. 
The levers operating these and the brake are on the plat¬ 
forms at the ends of the car. 

It has been seen that by means of the motor an electric 
current may be changed to mechanical energy. 

In the passage of an electric car down a grade or hill 
the current is turned off, but the forward motion of the 
car keeps the armature of the motor revolving. 

The motor is now a dynamo for it now receives mechan¬ 
ical energy from the effects of gravity, and hence generates 
an electric current. 

This electric current produces a consequent magnetic 
and electric attraction, which in accordance with Lenz’s 
Law operates to oppose the motion of the car. 

The motor thus operates as a brake. 


THE END. 



HELPS AND AIDS IN TEACHING HISTORY. 


Chase S ‘ The Land We Live In. Questions and Answers 

on its History. Three Parts in One Volume. The series includes a 
comprehensive review of the history, civil government, institutions 
and resources of the United States, that is invaluable to every 
teacher and student of American history. 

The author, one of the most careful students of History, says in 
his preface: “ My ambition is to excell all competitors in precision 
and completeness of statement, and in careful selection and arrange¬ 
ment of topics, according to relative importance.” 

It contains a more explicit treatment of the course of events since 
1850 than the school histories venture to give, and its statements will 
be found altogether trustworthy. Nothing of importance is slurred 
over. Price, 200 pp., boards. 40c. 

Ensign’s Outlines, Tables and Sketches in U. S. History. 

Teachers’Edition, the best and most complete outlines in United 
States History published. The outlines systemize the matter and 
are an aid in studving the subject from a variety of books. It can 
be used for ail cla'sses. Thirty-six thousand copies of this work have 
been sold and the demand is now greater than ever. Thisbookis, 
however, used by thousands of pupils in all parts of the country, 
including many of the leading schools of the city of Chicago. Low 
rates given for'quantities. Price, 25c. By the doz., &2.25, prepaid. 

Ensign’s History Outlines, Pupil’s Editions. An Out¬ 
line and Note Book for Pupils of Advanced Grades. Contains Out¬ 
lines, Notes. Questions and Suggestions, Blanks to be filled by the 
Pupils, Skeleton Maps of Important Campaigns, List of Cabinet 
Officers, Chart Showing Times and Duration of Power of all Political 
Parties, etc., etc. Also 24 pages blank paper for additional notes. 
Price.20c. 

An Outline and Note Book for Pupils of Grammar Grades. 

Practically the same as above but with notes and outlines less full, 
*nd no blank sheets. Excellent for country schools and grammar 
gradesof city schools. Price .15c. 

Ensign's Outlines in Ancient and Modern History. 

New Edition. Just out. Contains 200 pp. of Outlines, Notes and 
Maps, all difficult names respelled or diacritically marked. Also 80- 
blank pages through the book for notes. Bound in boards. The 
best and most complete outline in Ancient History published. 
Price.. 


Freeman’s General History Cards, a set of 136 cards. 

Seven Hundred interesting Facts about Persons, Events, Dates, Bat¬ 
tles Countries, Religions, Places, Movements. Wars, of all Nations. 

The statements are perfectly reliable, and gathered from the best 
authorities. 

They may be used by any number of persons at the same time. 

They develop in a wonderful degree the ability to tell what one 
knows at a moment’s notice. 

Put up in a neat box with full directions for use at home and in 
school. Price, prepaid.:...50c. 

Improved Historical Cards. Two hundred—each show¬ 
ing at the top the name of some prominent character in United 
States history, some important battle or other event. 1 here are 
following from five to ten salient points about the name at the head. 
Thousands of boxes sold and customers use them until “they wear' 
out.” Price.. 


A. FLANAGAN, Chicago. 










HELPS AND AIDS IN TEACHING HISTORY. 


Hunter's Historical Games With Cards. On the history 

of the United States. Ten editions have been published. Children 
are delighted with them, and are thus induced to study history with 
a new zeal. The noon-hour can be passed pleasantly and profitably 
in playing Historical Games and searching the books for events sug¬ 
gested on the cards. Full directions w ith each box for playing 22 
games. Price,.40 c ^ s * ne U 

Early History Stories of North, South and Central 

America. Their discovery and settlement. Illustrated with over 
fifty wood engravings. Contents include stories about such charac¬ 
ters as Leif, the Lucky; IIow Columbus found a New World; Span¬ 
ish Cavaliers’ Fountain of Youth; How Mexico was Conquered; 
Seven Cities of Cibola, and many others. Thirty-two stories in all 
about the Early Discoveries of North, South and Central America. 
Every pupil and teacher will have a new desire for history after 
reading the daring adventures, the thrilling escapes, the cruel hard¬ 
ships endured and perpetrated by the discoverers and founders of 
the Three Americas. Excellent supplementary reading of history 
work. May be returned if not perfectly satisfactory. Boards, 200 
large pages, 40o. Cloth, 200 pp., 60c. 

Rice’s Course of Study In History and Literature. 

With suggestions and directions. By Emily J. Rice, of the Cook Co. 
Normal School. This little pamphlet is the result of w r ork in the 
schoolroom. The author, under direction of Francis W. Parker, has 
prepared a course of study that combines the subjects of History and 
Literature. It contains the most complete outline published of 
workson literature and history combined. Excellent lists of refer¬ 
ence books given for each grade. Price.20c. 

Salisbury's Skeleton Maps. By Albert Salisbury’, White- 

water (Wis.) Normal School. 

An Aid to Teaching United States history and geography. 

These Maps are printed outlines or skeletons. They may be used 
in Geography or History; the pupil tilling in as maybe required. 
Much more w'ork can be done this way than with the common 
method. Each map is printed a light blue on w r hite paper 12x18 ins. 

No. 1 is of the United States, and is intended for general use. 

No. 2 is of the Atlantic States, and is for work in the Colonial and 
Revolutionary periods of United States History. Price,25 cts.per doz. 

Trainer’s How to Teach and Study United States History. 

This book contains a complete exposition of original and successful 
methods of teaching United States History. Proceeding upon the 
assumption that the student should remember Important Facts, the 
author presents by means of admirable Brace Outlines for the Black¬ 
board, a Series of Object Lessons in History—Lessons which appeal 
both to the eye and to the understanding. 

This w r ork also contains a Blackboard Analysis of each Topic in 
United States History, Directions for Teaching and Studying each 
Topic, Methods of Outlining, Written and Oral Reviews, 1,000 Ques¬ 
tions and Answers on United States History, Questionson Individual 
States, Individual Territories, Names and Mottoes of States, etc. 

It teaches a pupil how to study his lesson, how to tind the promi¬ 
nent facts needed, how to find Parallel authorities, how to remem¬ 
ber dates, etc. The Brace Outlines, w’hich are a prominent feature 
of the work, Fix Periods, Dates and Principles on the Mind with ease 
and photographic accuracy. They give a clear and intelligible out¬ 
line of all important topics; confusing, nonessential details being 
avoided. Price .-.IS cts. 


A. FLANAGAN, Chicago. 






















